What types of lever on backplate are there?

Lever lock sets are used in conjunction with a sash lock and key

Lever latches have plain back plates and are used on doors with tubular latches that do not lock

Bathroom sets which have a built in turn & release are used in conjunction with a bathroom lock.

Privacy sets have a built in turn & release which locks the handle and works with a tubular latch. The Privacy set is only available in some designs.