What is the meaning of Question_mark?

The punctuation mark "?", used at the end of a sentence to indicate a question.

A state of doubt or uncertainty.

An enigmatic, inscrutable, or mysterious person or thing; an enigma, a riddle.

Polygonia interrogationis, a North American nymphalid butterfly with a silver mark on the underside of its hindwing resembling a question mark (sense 1).

Final interrogative particle, expressing second-guessing, usually in an exaggerated, rising tone.

Source: wiktionary.org