The designation '4dxy' refers to a specific type of atomic orbital. In quantum mechanics, the '4' indicates the principal quantum number (n=4), specifying the energy level. 'd' represents the angular momentum quantum number (l=2), defining the shape of the orbital. The 'xy' subscript denotes a particular spatial orientation of the d orbital. There is only *one* 4dxy orbital for a given atom because the spatial orientation is unique for the given n and l values.