An asterism in Orion, formed from 7 stars. Not one of the 88 constellations.
A vast ring of six bright stars enclosing most of the winter sky, with Betelgeuse sitting off-centre inside it. The single best way to orient yourself on a January evening.
The Winter Hexagon is centred near right ascension 6.1 hours, declination +9°. It straddles the celestial equator, so it is visible from essentially anywhere on Earth at the right time of year.
The International Astronomical Union recognises 88 constellations, and they divide the whole sky between them like countries on a map. The Winter Hexagon is not one of them — it is a pattern picked out of Orion. That makes it an asterism: a shape people recognise and name, with no official standing whatsoever.
The distinction matters less than it sounds. Asterisms are usually easier to find than the constellations containing them, which is exactly why they survive.
SkyRef can draw the Winter Hexagon in its real position for wherever you are — switch on the asterism layer and it appears dashed across the constellations it runs through.