ChatGPT is an LLM (Large Language Model) trained by Open AI. GPT-3.5 is the technology behind Open AI's ChatGPT. GPT-3.5 is a text generation model designed to chat, in that when you give it a text question or prompt, it can generate the answer or a paragraph of following text. The model is able to answer questions on a wide variety of topics in multiple languages, and can even do complex math, and write code.