ChatGPT is GPT-3.5 Turbo.
3.5 Turbo is the ChatGPT model: it's cheaper (1/10th the price), faster and has a bunch of extra RLHF training to make it work well as a safe and usable chatbot.
https://openai.com/blog/introducing-chatgpt-and-whisper-apis introduced the turbo model.
ChatGPT is GPT-3.5 Turbo.