Definition of pistons:
(n) :
(mechanics) A solid disk or cylinder that fits inside a hollow cylinder, and moves under pressure (as in an engine) or displaces fluid (as in a pump)
(n) :
(music) A valve device in some brass instruments for changing the pitch
(v) :
(intransitive) To move up and down or in and out like a piston.
(n) :
A surname.