While it may sounds like business hours to some this is an industry standard way of describing the circuitry and function of relays, switches, etc. When I first started in this industry the meaning of these phrases confused me but now that I know what they mean it seems so simple. 

Normally Open is when the circuit is open or in other words off. So when you hear normally open it basically means that it is momentary on. So it is off all the time unless the switch or relay is in use and then it "closes" the circuit to turn it on and when released it returns to the off position. For example a window switch in your car, it usually only opens or closes when you are pushing the button down and when you release it it goes back to off. 

In contrast to that the Normally Closed means that it is on all the time and is momentary off. Only off when in use otherwise it is on constantly. 

Some relays have both functions available, snap action switches often have only a singular function. If you have any questions or are unsure of what you need please contact one of our seasoned professionals who can help you figure out exactly what you are looking for.