Shader
A small program run on the GPU, once per vertex or per pixel, massively in parallel.
Vertex shaders transform geometry; fragment shaders compute the colour of each pixel. Programmability replaced the old fixed-function rendering pipeline around 2001 and effectively enabled all modern graphics. Written in GLSL, HLSL or WGSL.
Compute shaders broke the idea free of graphics entirely: arbitrary parallel computation on the GPU. It is a short step from there to CUDA, and to the same hardware now being used mostly for matrix multiplication in neural networks.