Yax is the tenth of the nineteen periods of the Haab, the 365-day Maya solar calendar of eighteen twenty-day months plus a final five-day period. Recorded here by its Yucatec name, Yax, glossed as the green or first storm, yax meaning green, blue, and new, the month is known from the colonial sources and the Classic inscriptions. Like each of the eighteen full months it counts twenty days, a Maya date naming the day by its place within the month together with its Tzolk'in day. Yax belongs to the colour-named run of months, Chen, Yax, Sak, and Keh, through the middle of the year. These are the features of the Maya solar calendar, one of the two interlocking cycles that turn together in the fifty-two-year Calendar Round of Maya timekeeping.
Yax, the tenth month, uses the same word that opens Yaxkin's name, generally translated as green or new, and its glyph in Classic inscriptions is understood by most epigraphers to relate to that same sense of freshness or renewal rather than encoding an unrelated meaning, though, as with several Haab month names, the precise semantic range intended by Classic scribes is inferred from later Yucatan usage rather than fixed by an unambiguous Classic-period gloss. The month falls in the latter part of the annual cycle of eighteen twenty-day periods, before the calendar moves into the final months preceding Wayeb, the five unlucky closing days, and, like every Haab month, its calendrical date slid gradually against the true solar seasons over long spans because the 365-day count carries no leap-day correction.