A CPU is usually the brain of a computer. A GPU is a visual processing unit, or graphics card that aids in rendering digital images on a monitor or other display device. GPUs are mostly used in gaming consoles, especially for graphic-intensive video games, which are also capable of running on PCs with low-to-medium specifications when they are not being used by gamers.
GPUs were invented for use with computers to accelerate the tedious calculations involved in 3D rendering applications including computer-aided design (CAD), architectural modeling, and engineering simulations. Computers using these applications render these images in an offscreen buffer called a frame buffer that can then be displayed on-screen without any visible loading time.