Web beacon

A web beacon is an object embedded in a web page or email, which unobtrusively (usually invisibly) allows checking that a user has accessed the content. Common uses are email tracking and page tagging for web analytics. Alternative names are web bug, tracking bug, tag, or page tag. Common names for web beacons implemented through an embedded image include tracking pixel, pixel tag, 1×1 gif, and clear gif. When implemented using JavaScript, they may be called JavaScript tags. 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.