Pixel is a term that refers to the basic element of a graphic image. In fact, the word pixel is short for Picture Element. Each image is made of a number of pixels, which is what determines not only its size, but also its quality. In the world of affiliate marketing, the word pixel refers to a 1x1 point, which serves as a tracking device that records the exact number of impressions. The tracking pixel loads every time a user opens a website or an email. Tracking pixels are used for gathering data thats essential for analyzing the performance of an online marketing campaign.