When we talk about normally open and normally closed, we may think we are referring to the door, but in electric locks we are referring to the state of the circuit.
In other words, NO (normally open) means that 99% of the time the circuit is open, it is not powered and only 1% of the time it is powered to open the lock; this philosophy typically applies to Fail Secure systems.
Fail Secure: If there is no power, the lock will remain closed
However when we talk about NC (normally closed) means that 99% of the time the circuit is closed, the lock will be powered. And 1% of the time it will no longer be powered to open the lock.
This system is designed so that in the event of a power failure or emergency, the lock can be exited; this philosophy is typically applied to Fail Safe systems.
Fail Safe: In the event of a power failure the lock will remain open.