1. Of a motor, to increase very quickly or suddenly in rotational speed. Every night, at exactly 2 AM, I hear the sound of motorcycle engines revving up outside my house.
2. To increase the speed of a motor, usually a motor, very quickly or suddenly. In this usage, a noun or pronoun can be used between "rev" and "up." The driver beside me started revving up his engine while we waited for the light to turn green, egging me on to engage with him in a road race. Don't rev the motor up like that—it's really disturbing for everyone who lives in this neighborhood.
3. To begin rapidly increasing in intensity, activity, or amount. Sales of the product were pretty low for the first few months, but they really revved up once that famous rapper started talking about it on social media. Public interest in the election began revving up after one of the candidates made some controversial remarks during a radio interview.
4. To cause something to begin rapidly increasing in intensity, activity, or amount. In this usage, a noun or pronoun can be used between "rev" and "up." We started revving production up after it became clear that there was great public demand for the toy. We need to find a way to rev up public engagement with this issue.
mod. excited, perhaps by drugs. The kids were all revved up, ready to party.