A pixel is what makes up the images displayed on your computer. They are minute dots of colour, which all together make up an image.
In online advertising, a pixel is often used to attach code to an ad, as it is the smallest possible thing a webpage will load. It is commonly referred to as a 1×1 as that is the dimensions of a single pixel.
Author: Justin Driskill
Justin is the founder of The Online Advertising Guide and a freelance Digital Projects Manager.