In the Aztec (Mexica) culture, the Nahuatl word nēmontēmi refers to a period of five intercalary days inserted between the 360 days labeled with numbers and day-names in the main part of the Aztec seasonal calendar.
Spanish lexicographers glossed it as dias baldios, "wasted days".
The interpretation is that the Mexicas considered the days unlucky, and most activities (including even cooking) were avoided as far as possible during the nēmontēmi period; however this interpretation is contested by Indigenous people.
According to Tunnicliffe (1979)[4] the Aztecs dealt with the remaining fractional-day discrepancy with the true tropical year length by adding a trecena (13 days) after each bundle of 52 years.
[4] A notable Indigenous leader born in the Nemontemi, was the Cuauhtemoctzin, one of the last tlahtoani of Mexico-Tenochtitlan.