Double Pole Double Throw. These have two rows of change-over terminals.
Equivalent to two SPDT switches or relays actuated by a single coil. Such a
relay has eight terminals, including the coil .
Double Pole Single Throw. These have two pairs of
terminals. Equivalent to two SPST switches or relays actuated by a single coil.
Including two for the coil, such a relay has six terminals in total. The poles
may be Form A or Form B (or one of each).