An object or sound vibrates when it moves back and forth quickly.
When we say something vibrates, we usually mean that it's moving up and down rapidly. This can happen to all sorts of things: a guitar string when you pluck it, your phone when it rings with a song on the ringtone setting, or even the ground during an earthquake. People who work with machines often talk about vibrations too - for example, if a car engine is vibrating, it might be a sign that something's wrong inside the engine.
The setting, on a portable electronic device, that causes it to vibrate rather than sound any (or most) needed alarms.
Example: Please put your cellphones on vibrate for the duration of the meeting.
To shake with small, rapid movements to and fro.
