Proper noun
A placename.
(astronomy, physics) The first generally accepted and confirmed black hole. A black hole in a high-mass X-ray binary (HMXB) with a blue supergiant companion (HD 226868), located in the constellation Cygnus.
(astronomy, physics) The high-mass X-ray binary star system containing this black hole and blue supergiant star.
Source: en.wiktionary.org