Second Lowest Unoccupied Molecular Orbital (SLUMO).
Note:
Subjacent and superjacent orbitals sometimes play an important role in the interpretation of molecular interactions according to the frontier orbital approach.
Source:
PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 513 (https://doi.org/10.1515/pac-2018-1010)