web beacon

or Web beacon

noun Digital Technology.

a very small graphic image or other object embedded in an HTML-formatted web page or email, used to track the online actions and activity of users: Web beacons that monitor customer preferences.

Nearby words

weaver's hitch, weaverbird, web, web 2.0, web address, web beacon, web browser, web crawler, web design, web designer, web developer

Also called web bug.