The Nahuatl term for the Aztec skull racks mentioned in Day of the Dead history is tzompantli.
A tzompantli was a wooden rack or palisade used to display human skulls, often those of war captives or sacrificial victims. The practice was documented among several Mesoamerican civilizations, but the best-known examples were associated with the Mexica (Aztec) capital of Tenochtitlan.
The largest and most famous example was the Hueyi Tzompantli, or Great Skull Rack, near the Templo Mayor. Spanish accounts described enormous displays, while modern excavations in Mexico City have uncovered skull racks and circular skull towers. The exact meaning of the Nahuatl word is debated, but translations include “skull rack,” “wall of skulls,” or “skull banner.”
A tzompantli is not the same thing as a modern sugar skull, or calavera de azúcar. Sugar skulls belong to contemporary Día de Muertos traditions, whereas tzompantli refers to an ancient ritual and political display connected with sacrifice, warfare, and religious power.