GA4 Glossary: 80 Terms Every Analyst Needs to Know (2026)

A

Active user — A user who has had at least one engaged session (10+ seconds, 2+ page views, or key event) in the selected date range. GA4's default user metric. Different from UA's "users" (which counted any user with at least one session regardless of engagement).

Ad_personalization — A Consent Mode V2 parameter controlling whether GA4 can use data for personalised advertising. Must be set to 'denied' by default for EU/UK users until consent is granted.

Ad_storage — A Consent Mode V2 parameter controlling cookies used for advertising measurement (gclid, ad attribution). One of the four V2 parameters.

Ad_user_data — A Consent Mode V2 parameter (new in V2) controlling whether user data can be sent to Google for advertising purposes. Required for modelled conversion filling to activate.

Analytics_storage — A Consent Mode V2 parameter controlling GA4's measurement cookies. When denied, GA4 sends cookieless pings in Advanced mode.

Attribution model — The rule used to distribute conversion credit across touchpoints in a user's journey. GA4 supports: Last click, Data-driven (default for qualifying properties), First click, Linear.

Audience — A defined group of users based on dimensions, metrics, or event conditions. Audiences build over time, can be published to Google Ads for targeting, and have membership durations up to 540 days.

Audience trigger — An event that fires the first time a user joins an audience. Used to create micro-conversion signals for Smart Bidding.

Auto-tagging — Google Ads feature that appends gclid to landing URLs automatically, enabling GA4 to attribute sessions to specific Google Ads campaigns without manual UTM parameters.

B

BigQuery — Google's cloud data warehouse. GA4's BigQuery export sends raw, event-level data daily, enabling unsampled SQL analysis. Essential for large properties and custom attribution modelling.

Blended (reporting identity) — GA4 reporting identity mode that uses User-ID first, then Google Signals, then device ID to stitch cross-device user journeys. Default for most properties.

Bounce rate — Not a native GA4 metric. The inverse of engagement rate (1 - engagement rate) is the closest equivalent. A session "bounces" in GA4 terms when it fails to meet engaged session criteria.

C

Cardinality — The number of unique values a dimension has. GA4 limits custom dimensions to ~500 unique values per day in standard reports; values beyond this appear as (other). High-cardinality data belongs in BigQuery.

Client_id — GA4's pseudonymous device identifier, stored in the _ga cookie. Format: XXXXXXXXXX.XXXXXXXXXX. Used to identify a device across sessions. Different from User-ID (which is assigned by you).

CMP (Consent Management Platform) — A tool that manages cookie consent and implements Consent Mode V2. Examples: Cookiebot, OneTrust, Usercentrics, Complianz.

Consent Mode — Google's API for adjusting GA4 and Google Ads tag behaviour based on user consent. V2 (required for EU/UK Google Ads since March 2024) adds ad_user_data and ad_personalization parameters to V1's analytics_storage and ad_storage.

Conversion — In GA4, a conversion is an event marked as a key event. Previously called "goal" in UA. Key events appear in the Conversions column in reports.

Cross-domain tracking — Configuration that links user sessions across two different registered domains, preventing them from appearing as new sessions. Implemented by adding both domains to GA4's "Configure your domains" list.

Custom dimension — A user-defined dimension registered in GA4 Admin that makes custom event parameters or user properties available in standard reports. Must be registered before data appears in reports (not retroactive).

Custom metric — A user-defined numerical metric registered in GA4 Admin, enabling business-specific values (margin, score, MRR) in reports.

D

Data-driven attribution — GA4's ML-based attribution model that distributes conversion credit based on the actual contribution of touchpoints to conversion, rather than arbitrary rules. Requires 300+ conversions and 3,000+ clicks per month.

DataLayer — A JavaScript array used to pass structured data to Google Tag Manager. The recommended mechanism for sending business data (transaction details, user tier, form IDs) to GA4 via GTM.

Data retention — The period GA4 stores event-level data accessible in Explorations. Default: 2 months. Maximum: 14 months. Change immediately on new properties. Not retroactive.

Data stream — A source of data flowing into a GA4 property. Types: web, iOS app, Android app. A property can have multiple streams (one web, one iOS, one Android) sharing the same property ID.

DebugView — A GA4 Admin feature showing real-time events from devices in debug mode (GTM Preview or Chrome extension). Displays individual event parameters — the primary tool for implementation validation.

Device-based (reporting identity) — GA4 mode using only the device cookie for user identity. No cross-device stitching. Most similar to Universal Analytics behaviour.

E

Engaged session — A session meeting at least one of: duration ≥ 10 seconds, 2+ page views, or 1+ key event. The basis for GA4's engagement rate metric.

Engagement rate — Engaged sessions ÷ total sessions. Ranges 55–80% for most properties. Not the inverse of UA bounce rate (though related). Introduced in GA4; doesn't exist in UA.

Engagement time — The total time GA4 estimates a user was actively engaging with the page (tab in focus). Different from session duration. More accurate proxy for actual reading time.

Enhanced conversions — A Google Ads feature that sends hashed first-party data (email, phone, name) alongside conversion events, improving attribution for cookieless or consent-rejected conversions. Target match rate: 70%+.

Enhanced measurement — GA4's automatic event collection (page views, scrolls, outbound clicks, site search, video engagement, file downloads, form interactions, history changes) enabled via toggle, without code. Can conflict with custom implementations if both are active for the same event type.

Event — The fundamental unit of GA4 measurement. Everything is an event: page views, clicks, purchases, scrolls. Events have a name and up to 25 parameters.

Explorations — GA4's flexible analyst workspace with 7 analysis types (Free Form, Funnel, Path, Segment Overlap, User Explorer, Cohort, User Lifetime) not available in standard reports. Requires Analyst access.

F, G

Firebase — Google's mobile app development platform. The Firebase Analytics SDK powers GA4 app tracking (iOS and Android). Events tracked via logEvent() appear in GA4 app data streams.

First-party cookie — A cookie set by the domain the user is visiting (e.g., _ga set by your domain). Survives longer than third-party cookies. Server-side GTM sets GA4's _ga cookie as a server-set first-party cookie, bypassing Safari ITP's 7-day cap on JS-set cookies.

Funnel Exploration — A GA4 Exploration type showing step-by-step conversion paths. Supports open (enter at any step) and closed (must complete step 1 before step 2) funnels.

GCD parameter — A URL parameter in GA4 network requests encoding the consent state at the time of the hit. gcd=11t = all consent granted; gcd=11l = denied, Advanced mode active; gcd=11p = denied, Basic mode.

GCLID — Google Click ID. Appended to landing URLs by Google Ads auto-tagging. GA4 reads gclid to attribute sessions to specific Google Ads campaigns.

Google Signals — Optional GA4 setting that uses signed-in Google account data for cross-device identity stitching. Required for Blended reporting identity. Consent-dependent.

GTM (Google Tag Manager) — A tag management system that deploys GA4 and other tracking tags via a web interface, without requiring code changes. The recommended implementation method for most websites.

H, I, K

Hit — The generic term for any data point sent to GA4 (page view, event, etc.). In GA4's context, usually called an "event."

Internal traffic filter — A GA4 data filter that excludes sessions from specified IP ranges (office, agency) from reports. Prevents internal browsing from inflating metrics.

ITP (Intelligent Tracking Prevention) — Safari's privacy feature that limits JavaScript-set cookie lifetimes to 7 days. Affects GA4's _ga cookie, making returning Safari users appear as new users after 7 days. Server-side first-party cookies bypass this limit.

Item — An element in GA4's e-commerce items array. Must include item_id, item_name, price, and quantity. Item_id must match the product ID in Google Merchant Center for Shopping campaign alignment.

Key event — A GA4 event marked as commercially significant (Admin → Events → Key event toggle). The GA4 equivalent of a UA Goal. Powers the "key event rate" metric and Smart Bidding conversion goals.

Key event rate — Key events ÷ sessions × 100. The conversion rate equivalent in GA4. Replaces UA's "Goal conversion rate."

L, M

Landing page — The first page of a session. GA4's Landing Page report shows sessions, engagement rate, and key event rate for each first page — enabling content performance and paid traffic quality analysis.

LookML — The modelling language used by Looker (the enterprise BI platform) to define dimensions, measures, and data relationships. Used to model GA4's BigQuery export into business-friendly reports.

Looker Studio — Google's free dashboard and reporting tool. Connects directly to GA4 via a native connector. Limited to standard aggregated metrics (same sampling as GA4 UI). Different from Looker (the paid enterprise BI platform).

Measurement ID — The GA4 property identifier in format G-XXXXXXXXXX. Placed in the GA4 configuration tag in GTM or directly in gtag.js. Different from the numeric Property ID.

Measurement Protocol — An HTTP API for sending events to GA4 from servers. Used for offline conversions, CRM stage updates, and backend events that can't be captured client-side. Requires client_id from a prior client-side interaction.

Membership duration — The length of time a user remains in a GA4 audience after qualifying. Configurable from 1 to 540 days. Shorter for urgency-based remarketing; longer for look-alike seed lists.

Modelled conversions — Google's ML estimates of conversions that would have occurred from non-consenting users (Consent Mode V2 Advanced mode required). Appear in Google Ads Conversion reports as a separate labelled count.

P, R

Parameter — A key-value pair attached to a GA4 event providing context. Up to 25 parameters per event. Parameters are not reportable in standard reports until registered as custom dimensions.

Predictive audience — A GA4 audience based on ML-predicted user behaviour (purchase probability, churn probability, predicted revenue). Requires 1,000+ purchasers and 1,000+ non-purchasers in 28 days to activate.

Privacy Sandbox — Google's initiative replacing third-party cookie capabilities with privacy-preserving Chrome APIs (Topics API, Protected Audience API, Attribution Reporting API). GA4 itself is largely unaffected as a first-party tool.

Property — A GA4 configuration entity that collects data from one or more data streams. Properties have their own Measurement ID, reports, and admin settings. Distinct from the Google Analytics account (which can hold multiple properties).

Realtime report — GA4's report showing users and events from the last 30 minutes. Updates every ~60 seconds. Shows event names and counts but not individual parameters (use DebugView for parameter detail).

Reporting identity — GA4 setting determining how user sessions are stitched across devices. Options: Blended (default), Observed, Device-based.

S

Sampling — GA4's practice of analysing a subset of data when volume is high, and extrapolating to total. Indicated by a shield icon in Explorations. Standard reports generally not sampled. BigQuery export is unsampled.

Segment — A filter applied to an Exploration that restricts analysis to users, sessions, or events meeting specified conditions. Different from Audiences (which build lists for remarketing) and Comparisons (which filter standard reports).

Server-side GTM (sGTM) — Google Tag Manager deployed on your own server infrastructure rather than in the user's browser. Enables first-party cookie setting (bypasses ITP), data stripping before forwarding to GA4, and reduced client-side JavaScript overhead.

Session — A period of user activity on your site or app. In GA4: begins with session_start event; ends after 30 minutes of inactivity. Does NOT reset at midnight (unlike UA). Campaign changes do NOT start a new session (unlike UA).

Session_start — The GA4 event fired at the beginning of each new session. Automatically collected. Unlike UA sessions, GA4 sessions don't reset at midnight.

Smart Bidding — Google Ads' automated bidding system that adjusts bids based on conversion probability signals. Powered by GA4 key event data imported as Google Ads conversions. Needs 30–50 conversions per campaign per month to function effectively.

T, U, V

Tag — Code (JavaScript or HTML) placed on a website to send data to analytics, advertising, or other platforms. In GTM, a tag is a configuration element pairing a code snippet with a trigger.

Transaction ID — Unique identifier for each purchase event. Must be unique per order. Duplicate transaction IDs cause revenue over-reporting. Should never be used as a GA4 custom dimension (high cardinality).

Trigger — In GTM, the condition that causes a tag to fire. Examples: page load, custom event, form submission, click on specific element.

UTM parameters — URL parameters (utm_source, utm_medium, utm_campaign, utm_content, utm_term) that attribute session traffic to specific campaigns. Inconsistent UTM naming causes (Other) in channel group reports.

User-ID — A stable identifier you assign to authenticated users, enabling GA4 to stitch cross-device sessions. Must be hashed before sending to GA4 (never send raw PII). Enables Blended reporting identity to function correctly.

User property — An attribute attached to a user in GA4 (e.g., subscription_plan, customer_tier). Persists across sessions until overwritten. Limit: 25 custom user properties per property.

User_pseudo_id — GA4's automatically generated pseudonymous user identifier (derived from the _ga cookie on web, app_instance_id on mobile). The primary user key in BigQuery export.

W

Wait_for_update — Consent Mode parameter specifying how many milliseconds to wait for a CMP to update the consent state before GA4 tags fire. Default: 500ms. Increase for slow-loading CMPs.