"Luminosity class" refers to a categorization of stars based on their brightness and size. It helps scientists understand a star's characteristics and where it is in its life cycle. Full definition
We present three new spectroscopic identifications, including a Be high mass X-ray binary (HMXB) or a gamma Cassiopeiae (Cas) system, a symbiotic X-ray binary and an O - type star of unknown luminosity class. (arxiv.org)
The Roman numerals used for Secchi classes should not be confused with the completely unrelated Roman numerals used for Yerkes luminosity classes. (en.wikipedia.org)