Normally Open/Close-NO/NC.,When a momentary push button switch is not actuated, it’s in a “normal” state. Depending on how the push button is constructed, its normal state can be either an open circuit or a short circuit. When a metal push button is open until actuated, it’s said to be normally open (abbreviated NO). When you actuate an NO switch, you’re closing the circuit, which is why these are also called “push-to-make” switches.
Conversely, if a button usually acts like a short circuit unless actuated, it’s called a normally closed (NC) metal switch. NC push button switches are “push-to-break”; actuating the switch creates an open circuit.
Among the two types, you’re probably much more likely to encounter a normally open momentary metal push button switch.