So, ... did you read my email?
A tracking pixel, is one of various techniques used on web pages or email, to unobtrusively (usually invisibly) allow checking that a user has accessed some content. Common uses are email tracking and page tagging for web analytics. Alternative names are web beacon
, web bug
, tracking bug
, tag
, or page tag
, pixel tag
, 1×1 gif
, and clear gif
. When implemented using JavaScript, they may be called JavaScript tags [1]
There is a work in progress to standardize an interface that web developers can use to asynchronously transfer small HTTP data from the User Agent to a web server that call it simply beacons (in the context of web development) which can be used to send data to a web server prior to the loading of the document without delaying the load and affecting the perception of page load performance for the next navigation [2].
The excerpt above has been retrieved from wikipedia.
[1] The Web Bug FAQ
[2] Beacon
[3] Source: Wikipedia