This page is about procedure. If you have just been accused and want to know what the number means and what to say first, read falsely accused of using AI — this one picks up after a written decision, when there is a formal process to run.
Regulations differ by institution and by country, so what follows is the shape most systems share rather than any one set of rules. Yours will be published, usually under "academic misconduct", "academic integrity" or "student appeals", and that document beats anything on this page where the two disagree.
Two systems are written up here in full. If you are at a UK university, the stages a UK appeal actually runs through replaces the generic version below, and nobody in UK higher education mandates AI detection — which matters when a panel describes running one as an obligation. If you are in India, the regulation your department is most likely citing is a plagiarism rule: the UGC's similarity bands, and why AI writing sits outside them.