What is Question mark?
Question mark definition and meaning on Dictionary terms:
Also called interrogation point, interrogation mark. a mark indicating a question: usually, as in English, the mark (?) placed after a question.
something unanswered or unknown: His identity is still a question mark to most of us.
an anglewing butterfly, Polygonia interrogationis, having silver spots shaped like a question mark on the underside of each hind wing.