GPU versus CPU

GPU stands for Graphics Processing Unit. Originally designed for rendering graphics and video but now used for other applications of parallel computing eg. machine learning.
The standard CPU uses sequential processing whereas the GPU is designed for parallel processing, specialising in performing many simple calculations simultaneously.
Harnessing the GPU requires specialised programming approaches.
Most standard laptops and desktops (if they are not designed for graphically-intensive tasks) incorporate graphics processing within the CPU. The CPU chip is on the same chip as the CPU chip. This is called integrated graphics processing.
Some laptops, especially those marketed for gaming or professional work, have a separate GPU chip. This is a more powerful graphics processor, separate from the CPU.