What Is a Large Language Model (LLM)? Plain-English Definition
Large language model (LLM): A large language model (LLM) is an AI system trained on very large amounts of text to predict and generate language. That lets it answer questions, summarise, draft, classify and translate. GPT, Claude, Gemini and Llama are examples.
What LLMs are good at
Reading and writing: summarising documents, drafting replies, extracting fields from messy text, classifying requests, translating, and following structured instructions.
Where they fail
LLMs can state wrong information confidently (often called “hallucination”), don’t know facts about your business unless you give them, and can be inconsistent. That’s why business systems ground them in your data (RAG), constrain what they can do, and keep a human in the loop for important decisions.
Choosing a model
Bigger models are usually more capable but slower and pricier. Many business tasks run well on smaller, cheaper models. We pick per task and re-test when providers update their models.
Related terms: RAG (retrieval-augmented generation) · Prompt engineering · AI agent