Tracking pixels (also called web beacons, web bugs, tracking bugs, web tags, page tags, pixel tags) are small 1 x 1 GIFs which are embedded in emails by marketers and some email companies to track the following:

  1. when did you open your email
  2. where did you open your email
  3. how many times did you open the email

You probably haven’t seen a tracking pixel, at least not with your naked eyes, because they can literally be a single 1 x 1 pixel image buried somewhere in an email.
They’re often completely invisible because they’re transparent.