Following is a diagram showing you different relay types.

The following animation shows a normally (NO) open relay in action

KEY
SPST (NO)- Single Pole Single Throw (Normally Open)
SPST (NO)- Single Pole Single Throw (Normally Closed)
DPST (NO) – Double Pole Single Throw (Normally Closed)
SPDT –Â Single Pole Double Throw (Normally Closed)
DPDT (NO) – Double Pole Double Throw (Normally Closed)