Graphics Processing Unit
A GPU or Graphics Processing Unit is a piece of computer hardware originally intended to speed up computer displays, but also used for speeding up other highly parallel processing jobs. Their relevance to Go is that they are often used in neural networks, as used by AIs such as LeelaZero and KataGo.
bugcat: This article originally said that AlphaGo ran on GPUs. In fact, it ran on tensor processing units (TPUs), described by Wikipedia as "AI accelerator application-specific integrated circuits (ASICs) developed by Google specifically for neural network machine learning".