A neural network trained on massive amounts of text to understand and generate human language. "Large" refers to the number of parameters (billions) and the size of the training data (trillions of tokens). Claude, GPT, Gemini, Llama, and Mistral are all LLMs.
Why it matters
LLMs are the technology behind every AI chat, code assistant, and text generator you use. Understanding what they are (statistical pattern matchers, not sentient beings) helps you use them effectively and recognize their limits.