The transformer — Use

What do the terms primary, secondary, step-up and step-down mean in relation to a transformer?

The primary coil is the input coil, connected to the a.c. supply; the secondary coil is the output coil, connected to the circuit that uses the transformed voltage. A step-up transformer increases the voltage from primary to secondary (secondary has more turns than primary); a step-down transformer decreases the voltage from primary to secondary (secondary has fewer turns than primary).