Huey tlatoani means “great speaker” and is commonly used for the supreme ruler of the Mexica Empire, such as Moctezuma II and Cuauhtémoc. The title shows the higher rank of the ruler of Mexico-Tenochtitlan over other rulers.
For learners, this is the term to connect with the highest Mexica ruler, especially when reading about the Spanish conquest and the fall of Tenochtitlan.