Tracking Pixel
Also known as: web beacon, 1x1 pixel
An invisible image used to silently report a page view or event back to a tracker.
A tracking pixel is typically a 1×1 transparent image whose URL contains identifiers (your user ID, the page you're on, the action you just took). When the browser loads it, the request itself is the signal.
Pixels work even when JavaScript is disabled, which is why they're still in heavy use for email open tracking, ad conversion attribution and analytics fallbacks. Blocking the host of the pixel cuts the signal.