This is a key for a LieAlgebra L, giving the list of generators. It can be seen by applying peekLie to L.
i1 : L=lieAlgebra{a,b,c}/{a b,a a b - a b c} o1 = L o1 : LieAlgebra
i2 : L.gensLie o2 = {a, b, c} o2 : List
The object gensLie is a symbol.