the difference between revving and accelerating ?

"Reving" is short for "revolving" so it refers to the driveshaft revolving inside the engine. It can be done in neutral or in drive.

Accelerating is the vehicle itself gaining speed.

Technically speaking, anytime a car accelerates, the engine revolves.

But coloquially, if someone says "they reved the engine" they probably mean the car was sitting still but the engine was "reving" or making noise because it was revolving.

Revving is when you are sitting at a light or in a parking spot revving your engine, annoying others around you, wasting fuel, spewing noxious fumes into the air that those around you must inhale or leave the area. Accelerating requires motion, once you start moving and increase fuel flow, the engine works harder and causes the vehicle speed to increase, accelerating above the previous speed.

One is all talk, and the other makes it happen

U should try revving an old car