In transition elements, the shells that are incompletely filled

Element which contain incompletely filled n^th shell and (n-1)^th shell in their atoms (or) in their most common oxidation state (+2)  are called transition elements Zn (Z=30)....[Ne]3s²3p⁶4s²3d¹⁰
Zn⁺²....[Ne]3s²3p⁶3d¹⁰
Zn and Zn⁺² have  completely filled 3d¹⁰ configuration.
Thus Zn is not a transition element.