Idle creep, sometimes called idle speed or just creep[citation needed] is the default speed that a vehicle with an automatic transmission will move either forward or in reverse when the change lever is in D for drive or R for reverse and the foot is taken off the brake pedal but the accelerator pedal is not depressed.
This behaviour is due to torque converter or clutch(es) being used in a vehicle.
Creep can be faked in vehicles without those mechanisms such as transmission-less fully electric cars by automatically applying throttle when creep is needed.
Manufacturers add fake creep to cars to make them feel more natural/traditional.
Similarly, shift steps are added to a continuously variable transmission to simulate the feel of a geared transmission and fake pre-recorded exhaust sounds are added to some electric cars to make them sound the way drivers expect.