GPT-4 is a natural language processing (NLP) system developed by OpenAI. It is the fourth version of the Generative Pre-trained Transformer (GPT) model, which uses deep learning to produce human-like text. GPT-4 is trained on a massive amount of text data and can generate text that is coherent and relevant to the given prompt. GPT-4 can be used for a variety of tasks such as summarization, question answering, translation, and text generation.