Voice over Internet Protocol, a.k.a. VoIP, is the transmission of voice traffic over a data network, e.g. the Internet.
It is a software-based phone system, hosted on a virtual server in a data centre, and available anywhere you have a good Internet connection.
An auto-attendant is a voice menu system that answers inbound calls and presents options to the caller. After listening to the options, the caller then responds by pressing a number corresponding to their choice.
A DID is a
Direct In-Dial number. You can have a single DID or a range of DIDs depending upon your requirements.
A Call Queue is a way to have multiple callers waiting in line to be serviced. They are used extensively by Inbound Call Centres and increasingly by smaller businesses to manage spikes in inbound calls to a small team of users. It allows you to keep the caller on hold much longer than if the phone was just ringing, as the caller is listening to music or some other self-promotional message.