The chin is the bottom part of the face. It is under the mouth and is the forward part of the jaw.
The chin is unique to present-day humans, our species. It is not present in the anthropoid apes, nor in any other hominin.Neanderthals did not have a human-type chin. In medical anatomy, the chin is called the "mental eminence".
Its absence in Homo floresiensis is grounds for thinking that small hominin was not of our species.