Toxcatl (Nahuatl pronunciation: [ˈtoːʃkat͡ɬ]) was the name of the fifth twenty-day month or "veintena" of the Aztec calendar which lasted from approximately the 5th to 22 May and of the festival which was held every year in this month. The Festival of Toxcatl was dedicated to the god Tezcatlipoca and featured the sacrifice of a young man who had been impersonating the deity for a full year.
The Toxcatl Massacre, a turning point in the Spanish conquest of Mexico, occurred when the Spaniards who were tolerated as guests in Tenochtitlan attacked and massacred the unprepared Aztecs during the celebration of Toxcatl. This caused the outbreak of open hostilities between the Aztecs and Spaniards, and during the Noche Triste a few weeks later the Spaniards fled the city.
The Aztec calendar was composed of two separate cycles—one of 260 days called the tonalpohualli (day count) and one of 365 days called the xiuhpohualli (year count).
The 365-day xiuhpohualli consisted of 18 twenty-day "months" (or veintenas), plus an additional 5 days at the end of the year. Some descriptions of the Aztec calendar state that it also included a leap day which allowed the calendar cycle to remain aligned with the same agrarian cycles year after year. But other descriptions state that the leap year was unknown to the Aztecs and that the correlation of the months to the astronomical year would change over time.
In any case, from the descriptions of Spanish conquistadors who witnessed the celebration of Toxcatl in 1521 we know that in that year the feast fell in our month of May.
According to Fray Diego Durán the name Toxcatl derives from the Nahuatl verb toxcahuia meaning "wither from thirst". Toxcatl then means "drought". Many other meanings have since been proposed for the name - many having to do with the necklaces of grilled maize that were worn by the revellers during the festivities. The Aztecs also used the name Tepopochtli (smoking or fumigation) to refer to the month of Toxcatl. The name of the corresponding month in other Mesoamerican cultures often have to do with smoke, steam or clouds. The Otomi word for the feast was Atzbhipi, bhipi meaning smoke. The Kaqchikel name was Cibixic, meaning "cloudy smoke". The Matlatzinca word for the feast however was Unditini meaning "we are going to grill maize".