Sucking

Creating a partial vacuum is called sucking. Infants are born with a sucking reflex, by which they instinctively know to suck for food. More generally drinking is partly done by sucking, and especially when drinking through a straw.

Breathing in involves the expansion of the lungs, with the result that air is sucked in.

The term "sucking" is also used for fellatio. "It sucks" means it is not pleasurable or functional at all.