A large language model, often shortened to LLM, is the engine behind chatbots like ChatGPT and Claude. It learned patterns of language by reading a huge slice of the internet, books, and articles, and it uses those patterns to predict what words should come next. It does not look things up in a database. It generates each answer on the spot, one piece at a time, based on everything it absorbed during training.
For example, When you ask a chatbot to write a birthday poem, a large language model is what strings the words together.