Access control is a system that grants, terminates, suspends, and limits access to any area you would like the keep secure. Usually this is done by some sort of device such as a transponder, RFID, fob, remote clicker, or access card.
Fail-secure devices are also called fail-locked or non-fail safe. In this configuration, applying electronic current to the strike will cause it to unlock. The strike would remain locked in a power failure, but typically the mechanical lock would still be able to be used to open the door from the inside. These units can be powered by alternating current, which cause the unit to buzz, or DC power which offers silent operation.
Fail-safe devices are also called fail-open. In this configuration, applying electric current to the strike will cause it to lock. Similar to magnetic locks, if there is a power failure, the door will open from merely being pushed or pulled. These types of locking devices are always operated with direct current.