The simplified definition for plagiarism is the copying and borrowing of another's original ideas and/or words. Plagiarism occurs with the inclusion of material not explicitly cited as well as with collaborative work from another student willfully or otherwise.
Each incidence of plagiarism is subject to review and consideration by the instructor, and is subject to a range of penalties including but not limited to failing the assignment, failing the course, and referral to the disciplinary review board (which may ultimately result in the expulsion, suspension, or disciplinary removal of the student from the university).
Be sure to check out the Citation Guide from Purdue Writing Lab for information on how to cite from sources in a variety of styles.
The Associated Press guidelines on AI use is that artificial intelligence tools cannot be used in the production of publishable content.
Other styles have released guidelines for citing AI. See those below.
Reference
OpenAI. (2023). ChatGPT (Mar 14 version) [Large language model]. https://chat.openai.com/chat