A large language model (LLM) is an AI system trained on enormous amounts of text to predict and generate human-like language. Models such as GPT, Gemini, and Claude power the chatbots, AI Overviews, and answer engines that now sit alongside — and increasingly in front of — traditional search results.
At its core, an LLM predicts the next most likely word (technically, token) given everything before it, one piece at a time. During training it absorbs patterns from billions of sentences; at the moment you ask a question, it isn't looking anything up in a database — it's generating a statistically plausible response from those learned patterns. That distinction explains a lot: it's why an LLM can write fluently on nearly any topic, and also why it can state something false with complete confidence, a failure known as a hallucination.
When a user asks ChatGPT "what's the best CRM for a small law firm?" and it names three tools with a short rationale, no blue links appear — yet brands were still recommended. Earning a place in that answer is a new discipline, one that overlaps with generative engine optimization. It rewards content that states facts clearly, earns third-party citations, and is easy for a model to parse and attribute.
Only up to their training cutoff, unless they're connected to live retrieval or web browsing. A standalone model can't know yesterday's news on its own.
Optimizing for these systems is the focus of SEO for ChatGPT, and it builds on the same foundations as machine learning.