A pixel is the smallest element of a computer screen that displays color. By extension, a pixel can also mean an image that measures one pixel per side – often, transparent.

In webmarketing, this image is stored on a web analytics server and requested when a hit is sent from a browser (for example, utm.gif for Google Analytics, or “collect” for Universal Analytics).

Due to misuse, the term has also grown to refer to the script that loads the pixel, and is thus sometimes a synonym for “tag” or “snippet”.

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