What is the difference between an executor and a personal representative in a will?

This is the answer I got when I asked the same question of a Probate Clerk.

An Executor is assigned by the writer of a will. If no Executor, a person has to file to be Administrator especially when no will. If the estate is under 20k, an affidavit is signed by a relative or interested party. This estate wil, not need probate. This is in the state of NJ.