GPU
A chip with thousands of small cores that work on many pixels at the same time.
See it in Shader forge. Pick the Plasma preset: every pixel of it is worked out on the GPU, every frame.
In plain words
GPU stands for graphics processing unit. It holds thousands of small, simple cores instead of a few big ones. That suits pictures, where the same small sum must be done for every pixel. A full screen has millions of pixels, and the GPU can colour them all many times a second. Phones, laptops and game consoles all have one.