The relay is sorted by the number of its throws. The knife of the relay is the common terminal of each path. The position of each relay's knife can be connected to the relay's throw. A relay can consist of n knives and m throws. For example, a single pole single throw relay (SPST) has a knife and a throw.
A type relay type A relay is single pole single throw type, its default state is "normally open".
Type C relays Type C relays are single pole double throw type, first with a relay throwing off, and then connected to another (first broken after the connection).
The only answer.
Type B relays Type B relays are single pole single throw type, the default state is "normally closed".
