Covalent bonding is stated as overlap of atomic orbitals .In ionic bonding the composite ions are held together by their electrostatic charges that result from the transfer of electrons from one atom to the other. What is exactly meant by "transfer" in terms of orbitals?
The "transfered" electron will be in an orbital that is mostly on the side of only one atom, i.e. the anion. That orbital will be slightly deformed by the presence of the cations around it, but no significant overlap with any of their outer orbitals (those which are as good as empty, because the electron has been lost to the other atom).
(Im writing "mostly" and "as good as" because there can always be a covalent contribution to the bond.)