For chemists, there exists a temptation to designate the orbitals comprising the first NTO pair (having the largest singular values λ i ) as "HONTO" and "LUNTO", in analogy to HOMO and LUMO. (The terms "HOTO" and "LUTO" have also been used occassionally. ) This seems to be especially prevalent in the literature on thermally-activated delayed fluorescence (TADF) emitters. As even some who use this terminology have acknowledged, this usage is incorrect insofar as "highest" and "lowest" are typically used in the context of the aufbau principle, whereas orbital energies are undefined in the NTO basis because the Fock matrix is not diagonal. As such, it makes no sense to discuss the energies of NTOs, and this makes the "HONTO" and "LUNTO" terminology especially confusing when discussed alongside HOMO/LUMO energy gaps, as is often done in the TADF literature. In this author's view, the terms "HONTO/LUNTO" should be avoided, so that visual descriptions of NTOs are kept separate from arguments based on oneelectron energy levels. In discussing the NTO pairs with the largest singular values, a more appropriate term is principle transition orbitals, or perhaps principle NTOs (pNTOs). The full set of NTOs can be labeled pNTO, pNTO -1, pNTO -2, . . ., in order of decreasing singular values