A language model (LLM) is a neural network trained on very large volumes of text to produce text by predicting, piece by piece, the most probable continuation. It does not consult a database of verified facts, and its knowledge stops at the end date of its training, unless it has access to documents or to a search.
Example
Asking an LLM to summarize a paragraph: it generates plausible text, with no guarantee that every detail is accurate.