ChatGPT is a natural language processing model created by OpenAI that can generate human-like responses to text-based conversations. It uses deep learning and was pre-trained on vast amounts of text to understand language. Performance is evaluated using metrics like perplexity, accuracy, fluency and human evaluation. There are ethical concerns around copyright, personal data, bias and how the training data was obtained. OpenAI has introduced a paid ChatGPT Plus subscription with additional features while maintaining the free version.