You may call me pedantic (and indeed I am!), but I've always taken the term "supergroup" to mean what it means here:
https://en.wikipedia.org/wiki/List_of_m ... upergroups. That is, "music groups whose members are already successful as solo artists or as part of other groups or well known in other musical professions": Cream, CSN(Y), Led Zep, Blind Faith, Humble Pie, ELP, and Bad Company being some well-known early examples, and Transatlantic, Them Crooked Vultures, Black Country Communion, and The Good The Bad & The Queen being some well-known recent examples, all of them included in that (very long!) list. (I'd have thought The Raconteurs and The Tangent would be on the list, too, but what do I know?)