Alnitak (or Zeta Orionis) is a double star system (spectral class O9I-b), located 817 lightyears from Sol, that makes up the third star in Orion's Belt, and is the location of at least one planet.
In circa 2030, a planet in this system was home to a writer who would write a classic theme to the words, "Let me help." He would recommend those words even over "I love you." (TOS: "The City on the Edge of Forever")
Background
A double star located in the constellation Orion, this system's name wasn't explicitly mentioned since Kirk simply pointed to the system and noted its location in the constellation. While we know which star he must've meant, it wasn't clear which nomenclature might be more commonly used, the older usage Alnitak or the constellation catalog name, Zeta Orionis.