Greeting the caller, reporting that all the operators are busy at the moment, plays music during waiting in queue, requests to stay on the line as the next available operator will pick up exactly your call.
Shared Extension is when a group of agents has one and the same extension line. During the incoming call the phone will ring at several agents simultaneously.
Mirrored Extensions is when you have one and the same extension line on several phones, in example, in the office, at home and on the cell phone. So when someone calls your extension all you phone sets sharing the same extension will ring.