ChatGPT is a language model that uses deep learning to generate human-like text. It is trained on a large dataset of text and uses a variant of the transformer architecture called the GPT (Generative Pre-trained Transformer) architecture. During training, the model learns patterns and relationships in the text data, allowing it to generate new text that is similar to the training data. When the model is used for generating text, it takes a prompt (a starting text) and generates a continuation of rhat text. The quality of the generated text depends on the quality of the training data and the complexity of the task.

In more eli5 terms:

ChatGPT is a computer program that can talk like a person. We teach it by showing it lots and lots of talking, like in books and on the internet. It learns how people talk and then it can talk like a person too. When you ask it something, it uses what it learned to try to say something that makes sense. It's like when you learn new words, you can use them to talk better.