1. ULX - Noun
2. ULX - Adjective
ULX (not comparable)
(astronomy) Abbreviation of ultra-luminous X-ray. (the individual X-rays are not ultraluminous)
(astronomy) Ellipsis of ultraluminous X-ray pulsar (“ULX pulsar”).
(astronomy) Ellipsis of ultraluminous X-ray source (“ULX source”).
Source: en.wiktionary.org