ggml is a library that provides operations for running machine learning models
llama.cpp is a project that uses ggml to run LLaMA, a large language model (like GPT) by Meta
whisper.cpp is a project that uses ggml to run Whisper, a speech recognition model by OpenAI
ggml's distinguishing feature is efficient operation on CPU. Traditionally, this sort of work is done on GPU, but GPUs with large amounts of memory are specialized and extremely expensive hardware. ggml achieves acceptable speed on commodity hardware.