ACD, or Automatic Call Distribution allows callers to be put on hold and connected to the first available agent.
A greeting designed to play outside of business hours. These often let customers know you are out of the office and what steps they should take to reach you.
Answering rules give you the ability to choose how incoming calls are handled.
Auto-Attendant or Custom Main Greeting Auto-Attendant
Auto-attendant (also referred to as custom main greeting) automatically greets and directs callers to the appropriate extension using a pre-recorded message chosen by you.