What is the meaning of ?

Used to indicate confusion or pondering when the speaker did not hear or comprehend clearly: huh; hmm; what; pardon?; what did (they/you/he/she) say?

Used to express doubt or disbelief: huh?; hmm?; what?; oh?; what do you mean?

Used to express subtle surprise or amusement/astonishment: huh!; oh!; what!

Used to express consent or agreement or approval: huh ok; oh alright; yeah; sure; ah yes

Source: wiktionary.org