Chen is the ninth of the nineteen periods of the Haab, the 365-day Maya solar calendar. Recorded here by its Yucatec name, Chen, glossed as the black storm and carrying the sense of a well or cave, the month is known from the colonial sources and, in its glyphic form, from the Classic inscriptions. Like each of the eighteen full months it counts twenty days, and a Maya date names a day by its position within the month alongside the interlocking Tzolk'in day sign and number. The month names Chen, Yax, Sak, and Keh form a set glossed by colours joined to storm or the year, marking a run through the middle of the Haab. These are the features of the Maya solar calendar, meshed with the sacred count in the fifty-two-year Calendar Round.
Chen, the ninth month, takes its name from the Yucatec word for a well or cenote, the same water-source term embedded in place names across the peninsula, including Chichen Itza, literally at the mouth of the well of the Itza. The etymological link to Chen's neighbour Mol, generally read as to gather, has led some scholars to treat the eighth and ninth months as forming a loosely related pair concerned with water in the Yucatec ritual year, though this reading is an inference from the two names' meanings rather than a connection stated outright in any surviving Classic or colonial text. As with the calendar's other periods, Chen's position relative to the true solar seasons drifted over the centuries because the 365-day vague year applies no leap-day correction.