An ancient form of Instant Messaging provided by Microsoft once used by all and sundry on the internet to real time communicate with others either by text or voice. Can also introduce the Webcam for more "intimate" discussions. Generally a way for Arrse members to get faster private messaging and/or flirt in real time!
Superceded by the likes of WhatsApp and Instagram... Circa 2019 that is...
One of its rivals is Yahoo Messenger