The Wizengamot try Harry and reluctantly dismisses the charges. From references in the book, it appears that a Wizengamot is like a Supreme Court of sorts. That is, references to "the whole Wizengamot" (in Percy's letter to Ron) imply that this type of trial is unusual.
Albus Dumbledore is a member of the Wizengamot. His membership is revoked for most of ...Order of the Phoenix, he is later reinstated.
Wizengamot is pronounced WIHZ-en-guh-maht in the audio CDs.