Valet mode refers to an option with a car's alarm system that allows the owner or driver to bypass the alarm system manually. Typically this bypass is used when the car is being valet parked so that the driver does not have to turn over her alarm transmitter to the valet parker.
Valet mode is typically activated either by a button on the key chain transmitter or by manually disarming the alarm system from within the car using the alarm system's valet switch. Once valet mode is established, the car's alarm ceases to work; however, the remote door locks and panic button are still operational. It is important to remember to re-arm the alarm system after picking up one's car from a valet parker.