What the title says. I've never heard that name for the temple used and have only ever heard it referred to as the Templo Mayor pyramid or Templo Mayor complex. Wikipedia redirects Huey Teocalli to the page for Templo Mayor, but it's otherwise not mentioned on the page, and google only brings up articles about the game itself.
"Templo Mayor" and "Huey Teocalli" both mean the same thing: Great Temple. The former is merely the Spanish translation of the Nahuatl. Huey means, basically, "great/grand," while teocalli is the term for "temple," derived from teotl (god/divine/supernatural) and calli (house). Another term also frequently used is teopan (place of the god/divine), which is frequently used to describe smaller shrines to other deities throughout the Sacred Precinct in the center of Tenochtitlan.
Of note, the term "Huey Teocalli" isn't much used in the earliest sources, instead the Great Temple is most often just referred to as In Teocal Huitzilopochtli (The Temple of Huitzilopochtli), the paramount deity of the Mexica. The pyramid was a double-temple, in the style of the Postclassic, with temples to both Huitzilopochtli and Tlaloc at the top though, so the more encompassing "Great Temple" nomenclature has become more common.