Normally open(NO) and Normally closed (NC) are terms used to define the states that switches, sensors or relay contacts are under when they are not activated.
A NO contact or a normally open contact is the one that remains open until a certain condition is satisfied such as a button being pressed or some other manner of activation such as those based on temperature, pressure, etc.
A NC contact or normally closed contact is the exact opposite of NO contact by function. It remains closed until a certain condition is satisfied.
