What does "Altare privilegiatum" mean exactly today?

Does anyone know what "_Altare privilegiatum_" means today? I mean, in former times it meant that the altar was privileged and one can get an indulgence. I also know, that for some of those altars, there had some renewals to be done by the Holy See. But what's the meaning of that today? A lot has changed even in church. Does this have any meaning at all today? If so, what's the meaning?