Irony is a type of comedy humor, where something that is supposed to be one way is the complete opposite.

Example from Get Fuzzy:

Bucky: If you drop that cake, Satchel, it will be on your head!

(Satchel drops the cake on Bucky's head)

Satchel: ...oh. How ironic.

Irony is viewed as one of the highest types of humor when correctly pulled off. However, if not used correctly, irony can also be just as un-hilarious.
