TeamSpeak is a VoIP solution that makes it easy for groups of people to join to chat online. TeamSpeak provides audio communication with other people thats perfect for in game chat. Some games don’t come with an in game live chat (both text bast and through a microphone) so gamers resort to renting TeamSpeak servers.
To host a TeamSpeak server you need a continuously running machine with a good internet connection. Renting a TeamSpeak server is a cheap way to take away the hosting responsibility. Usually TeamSpeak servers are in the dollars per month area and very cost effective.