An LLM (Large Language Model) is an artificial intelligence model trained on very large volumes of text to predict the next token in a sequence, which allows it to write, summarize, translate, reason and write code.
LLMs rely on the transformer architecture and range from a few billion to several hundred billion parameters. They are first pre-trained on raw text, then adjusted (instruction tuning, RLHF) to follow instructions and respect behavioral rules.
The best-known families are Claude (Anthropic), GPT (OpenAI), Gemini (Google), Mistral, Llama (Meta) and Qwen (Alibaba). They are used through an API or, for open-weight models, on one's own infrastructure.
Why it matters when hiring
Two very different jobs hide behind "LLM": those who train the models (research scientists and research engineers, scarce and concentrated in a few labs) and those who build products with them (AI Engineers). Clarify which one you need before writing the job ad. A good signal: the candidate talks about evaluation, costs and limits, not just demos.