Tracking
Pixel
1×1 image embedded in a confirmation page to fire a conversion.
A pixel is a tiny image (or JS snippet) loaded by the user's browser when they reach a thank-you page, firing a conversion event back to the ad platform. Browser-side, so subject to ad-blockers, ITP/ETP, cookie expiry. Most operators run server-side (postback) where possible and pixel only as backup.
Example
Meta pixel + Taboola pixel + GA4 event all fire on /thank-you. Postback fires from the offer's server. Belt-and-suspenders for attribution loss to ITP.