Side Keys
Side Keys are simply buttons on the side of the phone, designed to be used by your fingertips while holding the phone in your hand.
Modern smartphones typically have side keys that consist of a volume up/down rocker and a single lock/power button.
Some phones have additional buttons, which can often be customized to perform additional actions specified by the user. Common options include PTT and launching the camera.
See: PTT
Some phones have an additional switch for silencing alerts.