Ad tracking involves a lot of technical terminology. This glossary defines 50 of the most important terms in plain language, organised by category, so you can understand tracking concepts without needing a technical background.
Attribution
Attribution: the process of assigning credit for a conversion to one or more marketing touchpoints that preceded it.
Attribution model: the rule that determines how conversion credit is distributed across touchpoints. Common models include last-click, first-click, linear, time decay, position-based, and data-driven.
Attribution window: the time period after an ad interaction (click or view) during which a resulting conversion is attributed to that ad. A 30-day click window means any purchase within 30 days of a click is attributed to that click.
View-through attribution: attributing a conversion to an ad that was seen (not clicked) before the conversion. Used for Display and Video campaigns.
Click-through attribution: attributing a conversion to an ad that was clicked before the conversion. Standard for Search and Shopping campaigns.
Data-driven attribution (DDA): an attribution model that uses machine learning to assign conversion credit based on observed patterns in your account’s actual conversion data.
Last-click attribution: gives 100% of conversion credit to the final ad interaction before conversion. The default for most ad platforms.
Multi-touch attribution: any attribution model that distributes credit across more than one touchpoint in the customer journey.
Incrementality: the additional conversions caused by advertising, beyond what would have happened without the ads. The true measure of ad effectiveness.
Pixels and Tags
Pixel: a small piece of JavaScript code placed on your website that collects data about visitor behaviour and sends it to an ad platform (Meta Pixel, Google Tag, TikTok Pixel).
Base code / pixel base: the foundational JavaScript snippet that loads on every page, initialises the pixel, and fires the PageView event.
Event: a specific user action tracked by a pixel or analytics tool. Standard events include PageView, ViewContent, AddToCart, InitiateCheckout, Purchase.
Standard event: a predefined event name with a fixed set of parameters recognised by the ad platform. Opposed to custom events, which you define yourself.
Custom event: an event with a name you define that the platform does not natively recognise. Useful for tracking actions specific to your business that do not match standard event names.
Event parameters: additional data sent with an event. A Purchase event might include parameters: value (order total), currency, transaction_id, items (product details).
Google Tag Manager (GTM): a tag management system from Google. Lets you install and manage multiple tracking tags (pixels, analytics scripts) on your website without editing code directly.
Tag: in GTM, a tag is an individual tracking script (e.g. the Meta Pixel base code, or a Google Ads conversion action tag).
Trigger: in GTM, a condition that determines when a tag fires (e.g. “fire when URL contains thank_you”).
Variable: in GTM, a placeholder that retrieves dynamic values from the page or dataLayer (e.g. the order total from the Shopify dataLayer).
Server-Side Tracking
Server-side tracking: sending conversion events from your web server to the ad platform’s API directly, without using the visitor’s browser.
Conversions API (CAPI): Meta’s server-side API for sending conversion events. Also called Meta Conversions API or Facebook CAPI.
Enhanced Conversions (Google): Google Ads’ method of sending hashed customer data alongside conversion events to improve match rates.
Server-side GTM: a version of Google Tag Manager hosted on a server you control. Routes tracking events through your server before forwarding them to ad platforms.
Measurement Protocol (GA4): GA4’s API for sending events server-side to Google Analytics 4.
Event deduplication: preventing the same conversion from being counted twice when both a browser pixel and a server-side API send the same event. Achieved via matching event IDs.
Analytics
GA4 (Google Analytics 4): Google’s current analytics platform, using an event-based data model. Replaced Universal Analytics in July 2023.
Conversion: a completed goal action: purchase, form submission, phone call, account sign-up.
Conversion rate: conversions divided by sessions (or users). Measures how efficiently your store converts traffic into desired actions.
Engagement rate: in GA4, sessions where users were actively engaged (10+ seconds, 2+ pages viewed, or conversion occurred) divided by total sessions. Replaced Bounce Rate as the primary engagement metric.
Session: a group of interactions within a single visit to your website. In GA4, ends after 30 minutes of inactivity.
User: in GA4, a unique visitor. GA4 distinguishes between Total Users (any user) and Active Users (engaged users).
Funnel: the sequence of steps between a user’s first interaction and a conversion. Ecommerce funnel: visit → product view → add to cart → checkout → purchase.
Privacy and Consent
First-party cookie: a cookie set by the website the user is currently visiting. Less restricted by browsers than third-party cookies.
Third-party cookie: a cookie set by a domain other than the one being visited. Used for cross-site tracking. Blocked by Safari/Firefox and being phased out in Chrome.
ITP (Intelligent Tracking Prevention): Apple’s browser technology in Safari that limits cookie lifespans and third-party tracking.
GDPR: General Data Protection Regulation. EU privacy law requiring consent for data collection and processing.
Consent Mode v2: Google’s framework that modifies how Google tags behave based on user consent signals. Required for EU advertisers using Google Ads and GA4.
CMP (Consent Management Platform): a tool that collects user consent for tracking and communicates it to analytics and ad platform tags.
Identifiers
gclid: Google Click Identifier. A URL parameter appended when a user clicks a Google Ad. Used to attribute conversions back to the specific ad click.
fbclid: Facebook Click Identifier. URL parameter appended when a user clicks a Meta (Facebook/Instagram) Ad.
fbp: Meta’s first-party browser cookie, set when someone visits a website with the Meta Pixel. Used to identify the browser across sessions on the same device.
fbc: Meta’s click cookie, capturing the fbclid from a Meta Ad click. Used for attribution matching.
UTM parameters: URL parameters (utm_source, utm_medium, utm_campaign, utm_content, utm_term) that tag link sources so analytics tools can identify where traffic came from.
Event Match Quality (EMQ): Meta’s score (0–10) for how well conversion events are being matched to Meta user accounts. Higher EMQ = better attribution and optimisation.
SHA256: the hashing algorithm used to anonymise customer data (email, phone) before sending it to Meta CAPI or Google Enhanced Conversions.
Book your free Shopify tracking audit here and we will apply all of these concepts to your actual store setup, identifying exactly what needs to be fixed to get accurate conversion data.