Pixel art is a form of art where in individual pixels serve as building blocks for creating an image. It is similar to mosaic art in that small pieces are placed individually to create a larger piece of art.
Pixel art has existed since the day 2-D games with graphics came out. The term was first used by Robert Flegal and Adele Goldberg of Xerox PARC in 1982. While it was not called so at the time, pixel art was a way for game developers to create images using limited computing resources. Programmers had to work with each pixel to ensure that the entire image made sense. While technology has progressed and this technique is obsolete, this method of rendering images has carried on as an art style.