3 in this case would be your "index of the root;" please do not use the term "square root" in this case.
Note: 2^3 = 8 is a perfect cube.
Radical operator with index 3 of 8 would thus result in the cube root, 2.
∛8 = 2,
∛64 = 4,
and so on.
∛x is called "the cube root of x."