ChatGPT is a large language model that was developed by OpenAI. It is based on the GPT (Generative Pre-training Transformer) architecture, which is a type of transformer-based neural network. The model is trained on a massive amount of text data, and is able to generate human-like text by predicting the next word in a sequence based on the context of the words that come before it. ChatGPT can be fine-tuned for a wide range of natural language processing tasks such as language translation, text summarization, and question-answering. It can also be used in chatbots and other conversational AI applications.