Latching Relay
A relay that when set (either ON or OFF depending upon the relay configuration), locks into place until reset either manually or by a signal.

LCD
The abbreviation for Liquid Crystal Display.

LED
The abbreviation for Light Emitting Diode.

Line Drop
The drop in voltage along a power line caused by the resistance, reactance, and/or leakage in the line's wires.

Lock Relay Output
A relay on the controller that changes its state upon command by the controller, locking or unlocking a secure door.

Logging
Creating and storing a permanent record of events that can be reviewed, printed, and analyzed.