Alnitak is a triple star system in the constellation of Orion. It has the designations ζ Orionis, which is Latinised to Zeta Orionis and abbreviated Zeta Ori or ζ Ori, and 50 Orionis, abbreviated 50 Ori. The system is located at a distance of several hundred parsecs from the Sun and is one of the three main stars of Orion's Belt along with Alnilam and Mintaka.

The primary star, Alnitak Aa, is a hot blue supergiant with an absolute magnitude of −6.0 and is the brightest class O star in the night sky with a visual magnitude of +2.0. It has two companions—Ab and B, the latter known for the longest time and the former discovered recently, producing a combined magnitude for the trio of +1.77. The stars are members of the Orion OB1 association and the Collinder 70 association.