The vir is a massive parasite that stems from a single specimen with a certain measure of sentience. They were discovered by Roygaris Ursuul and Khali, the former gaining control of the vir itself and the latter gaining power over the vir's energy and control over that energy's distribution. Ursuul's access to the vir extended only to his family, and allowed the Ursuuls control over the vir itself, including suppressing another meister's vir, and removal of vir.
When the people of Khalidor pray to Khali, their goddess, she takes a small portion of their Glore Vyrden and siphons it into her "reservoir" of magic; she then returns however much she desires back to them via the vir, which acts as a channel to distribute the power. It is different from the Talent, but the extra energy from the vir takes control of all Talent-derived abilities, such as Dorian Ursuul's prophetic gift. The vir manifests in use as black, tattoo-like vines which rise out of the skin when in use. Their use is both magic and physical, but the base of the vir is in the arms, and spreads visibly the higher the user's skill and power with it. The Ursuuls are the only vir users who can hide their vir, no matter how much they possess; but, this gives them a weak point, as the vir needs a physical region (the neck) to emerge from, which can be blocked.