What are NO and NC on the AC contactor ?

AC contactor is a very commonly used electrical component in industrial control. Among the contacts of the AC contactor, in addition to the main contacts (both normally open contacts), there are also auxiliary contacts.

There are normally open and normally closed auxiliary contacts. There is a mark on the contactor body to distinguish the purpose of the auxiliary contact.

NC on the AC contactor means normally closed contact, NO means normally open contact.
The meanings of the letters are as follows:
N=NORMAL
O=OPEN
C=CLOSE
NO: Normal Open
NC: normal Close

Therefore, when we see the contactor and wiring, we can distinguish between NO and NC which is the normally open contact and which is the normally closed contact without using a multimeter.