The basics of tracking
Events
When a user lands on your website they trigger a number of events. Some of those events match 1:1 user actions, such as:
Page View
Form Submission
Add To Cart
Other events are auto-generated based on user behaviour matching predefined criteria such as:
Session Start
User Engagement
User Data
The exact rules when those events are defined and captured depends on the tracking solution. There are three main ways of capturing events:
Pixel auto-capture
Tag Managers (such as Google Tag Manager)
DataLayer
Those events become the data source and foundation for analytics and conversion tracking. Each event can carry additional information about user action. In addition to name it can carry data about what products user interacted with or what form fields were filled in. Those data-point are called event parameters and are essential for more advanced tracking scenarios.
Events are actions that happen within user's browser and in order to analyse them or optimize advertising campaigns based on them then need to be somehow sent to given tracking platform. That's why pixels were created.
Pixels
The name "pixel" is a historical thing. In the early days of internet advertising when using 3rd party cookies was a common practise most platforms where using tiny, transparent images (1 pixel big… or small) to load within tracked page and allow creating a 3rd party cookies. Other solutions included using iframes, but the overall idea was the same.
Over the years pixels evolved from simple images into small JavaScript libraries that can perform additional actions, such as capturing common events or parameters from the browser.
As 3rd party cookies are being slowly phased out by the advertising platforms, browser vendors and popularity of adblock add-ons, 1-pixel images aren't used anymore, but the name sticked.
Installing a pixel or more precisely JS code into a website means establishing a general connection between every visitor and their browser and given tracking platform. It involves creating or reading identifiers stored in cookies, performing basic tracking (for Page Views) or enabling auto-capture of common events.
Pixels are very generic piece of software that need to work on virtually any website, that's why even with auto-capture features the events coverage is very limited. It means installing a pixel won't take care of capturing more complex events like eCommerce actions with detailed product information.
Additionally, each pixel will work slightly differently and the tracked data can vary a lot between platforms. It means that not all events will be tracked.
Tags
To recap - event is something that happens on a website. Pixel is a piece of code that connects browser actions with advertising platform's systems and databases. Tags are a bridge between the two.
In other words a tag is additional, small piece of code dedicated only for the specific website and the specific action, such as add to cart. It allows defining precisely which user actions will be tracked.
Because, contrary to pixels that are generic and will work on all websites, tags are custom to very specific website they can track events and parameters more precisely.
If you think about all possible events and different content types that tags need to handle on a modern website managing those tags can be challenging, especially because every time a tag changes it needs to be updated on the page. That's why tag managers such as Google Tag Manager were created. Continue reading about them in the next chapter.
Tracking vs tagging
Tracking and tagging are often use interchangeably because their meaning is so similar, but there is a distinctive difference.
Tracking means nothing more or less than that the information about user action was sent to tracking system. It can be Google Analytics 4, Google Ads, Facebook or any other analytical or advertising platform that accepts stream of data. Tracking can happen via built-in pixel capabilities or via dedicated tags.
Tagging on the other hand means the all relevant tags were placed on a given website. Those tags, if implemented correctly, should ensure good tracking coverage.
In other words, tracking is the end goal of capturing data about user behavior, while tagging is a necessary step to get this data.