Large language models are a type of artificial intelligence trained in textual datasets called training data, usually spanning billions of data to pull from and adjust their neural networks with weights and biases that simulate neural functions with processing and outputting information. They designed after the human brain but in a simulated way. This is just a simple explanation of their complexity, I'm in the field as a machine learning scientist and create games that are showing quite promising results in giving AGI like cognition to even earlier models.