What is the difference between Normal Open and Normal Close?

A momentary footswitch  is in a normally open state or in a normally closed state. Some units require normal open or normal close. For example, depending on your delay unit, the delay tempo could be registering when the switch is released or when pushed. If you are uncertain of what type you should get, get the Skull Tap Tempo with Polarity Switch. This will toggle between normal open or normal close. Generally, normal open will cover most devices.