What it is
An LLM learns language patterns from a very large amount of text and, given an input, predicts the most likely continuation. That is where answers, summaries, code and translations come from.
Why it matters to an agency
The LLM is the engine behind your prompts and agents. Choosing the right model (by capability, speed and cost) affects the quality and the budget of your automations.
Example
When you paste a prompt into ChatGPT or Claude, the LLM is the one that reasons and produces the answer.