| Label | Type (orthogonal) | Label | Type (non-orthogonal) |
| AO | Atomic Orbital ("the" basis set of host electronic structure system). | ||
| NAO | Natural Atomic Orbital | PNAO | Pre-orthogonal* NAO |
| NHO | Natural Hybrid Orbital | PNHO | Pre-orthogonal NHO |
| NBO | Natural Bond Orbital | PNBO | Pre-orthogonal NBO |
| NLMO | Natural Localized Molecular Orbital | PNLMO | Pre-orthogonal NLMO |
| MO | Molecular Orbital (canonical; delocalized) |
*The pre-orthogonal orbitals (lacking only the final interatomic orthogonalization step of the NAO algorithm) resemble the idealized "textbook" shapes and their overlaps suggest the qualitative strength of orbital interactions.