It's important for you to understand what this terminology means, how it impacts you, the end user. Let's start at the beginning. Every computer monitor screen is made up of pixels. In fact, a pixel is the smallest unit of resolution on a video screen. Everything on the screen is formed of pixels.
More pixels are better, because the screen can display more detailed images.
In order for an image to be created on your screen all of your monitor's pixels need to be filled in with color. A graphics board acts as an interface between a computer's processor and the monitor. A graphics board helps get more information or data to a monitor in a faster and enhanced way, and, in the case of 3D graphics boards, also adds the 3D elements. Most old graphics boards could deliver ONLY 16 bits of information per pixel. With only 64,000 visible colors the pixels may not always blend together when forming the total image on your screen.