[to be fair, Cat also doesn't know why they're in the car. it's fine. he seems remarkably calm for a guy who doesn't know why he is here, though. and he doesn't seem to mind that a stranger is watching him work]

It's a term for starting the car's ignition without its keys.

[a beat. and then, a bit more cheekily]

In simpler terms. . . it's what someone does if they want to steal it.