In mathematics, especially in the area of abstract algebra that studies infinite groups, the adverb virtually is used to modify a property so that it need only hold for a subgroup of finite index.
Given a property P, the group G is said to be virtually P if there is a finite index subgroup
such that H has property P. Common uses for this would be when P is abelian, nilpotent, solvable or free.
For example, virtually solvable groups are one of the two alternatives in the Tits alternative, while Gromov's theorem states that the finitely generated groups with polynomial growth are precisely the finitely generated virtually nilpotent groups.
Gromov's theorem says that a finitely generated group is virtually nilpotent if and only if it has polynomial growth.