What is the difference between a normally open and a normally closed switch?
In switch language, open means to disconnect, or break the
circuit. Some people call this "turned off". Closed, is to connect,
or make the circuit. Some people call this turned on.
In the case of a normally open switch, the switch is open (off)
unless something takes action on the switch. Pushes a button for
example, or holds a magnet near the switch, or other active force.
A normally closed switch is closed (on) unless some force causes
the switch to be opened.