The word used to reply to a question or sentence you either did not understand, misheard, were confused by or you did not hear.
Similar to nes.
Dave: You done that homework?
Jonzy: Huh?, sorry I was looking at the seagulls outside.
Dave: Huh?
Jonzy: Yeah the seagulls are going fucking crazyout there!
<Joe> Yeah, so a tomato is a fruit, not a vegetable.
<Bob> Huh.
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<Eazy-E> I went to the hospital with a really bad cough, and the doctordiagnosed me with AIDS.
<Jerry> Huh.