What is the Mayan 260-day calendar called?

The Mayan 260-day calendar was called the Tzolk'in.

The Tzolk'in was the Maya sacred calendar, used to organize ceremonies, divination, and important ritual dates. It was not a solar year like the 365-day Haab', nor was it the Long Count, which recorded long spans of time from a fixed starting point. The Calendar Round was a larger cycle created by combining the Tzolk'in and Haab' calendars.

The Tzolk'in worked by interlocking a cycle of thirteen numbers with twenty named days. Because 13 and 20 are relatively prime, every number-and-name pairing took 260 days to recur. A date could therefore be expressed as a combination such as a number followed by a day name, with the sequence continually repeating.

Tzolk'in is the modern scholarly spelling; tzolkin is also common, and different Maya communities use names in their own languages. The calendar remains in use among some contemporary Maya communities, particularly in the Guatemalan highlands. Its original purpose is not settled: explanations include ritual scheduling, agriculture, human gestation, and astronomical or mathematical patterns.