A pusher (also called a push piece or button) is used to activate an internal function in a watch, typically a chronograph.
Most watches use a crown to control timekeeping functions, but many other complications are activated by other means. In chronograph watches, a "pusher" is the most common control mechanism. Typically extending out of the case at 2:00 and 4:00, the pushers start, stop, and reset the chronograph timing function. Some chronographs include another pusher to control a rattrapante hand, while other "monopusher" models use a single pusher co-axial with the crown. Bullhead models feature pushers at 11:00 and 1:00.
There are different styles of pushers: Some extend far out from the case ("pump pushers"), while others sit nearly flush or are shaped to integrate with the case or crown guards. Some watches are known for unusual pushers, including the 1980s Seiko Giugiaro chronographs which had cam-activated pushers extending far outside the case.