Some solenoids that need to generate high pulling power or have long throw, are wound with fewer turns / thicker wire ( more current draw / greater magnetic field ). This is OK for short duty cycles but they will burn up if kept at full power.

With PWM ( Pulse Width Modulation for others on this list ) , the circuit would apply full power to pull the solenoid in then , say after a second, rapidly pulse the output to reduce current ( and voltage ) If the pulses are rapid enough, the sol stays pulled in as the magnetic field to hold a sol in is usually lower than pull in.

PWM has a frequency ( how often the power is turned on and off ) and a duty cycle ( how long the power is on )

To clarify, the continuos duty of the KD sol I was speaking of would be when the car is idling at a stop light / sitting running warming up for who knows how long.