In plain English
Natural language processing is the branch of AI concerned with enabling computers to understand, interpret, and generate human language. It spans tasks such as translation, summarisation, sentiment analysis, and question answering. Large language models are the current high point of NLP, but the field is much older and broader than them.
A worked example
Automatic translation, predictive text, and tools that gauge whether reviews are positive or negative are all applications of NLP.
Common confusion
NLP is the broad field; a large language model is one powerful modern approach within it, not the whole of it.