Pop is the first of the nineteen periods of the Haab, the 365-day solar calendar of the Maya, which runs alongside the 260-day Tzolk'in. The Haab is built of eighteen months of twenty days each, followed by a short nineteenth period of five days; Pop opens the year. Its name means the mat, the woven reed mat that was a symbol of authority and the seat of a ruler, so the month carried associations of rulership and order. Recorded here by its Yucatec name, Pop, the month is known from the colonial sources and the Classic inscriptions alike. The turning of the year at the seating of Pop was marked by renewal and the refurbishing of household goods. These are the features of the Maya solar calendar, in which every day is named by its position in one of these nineteen periods together with its day in the interlocking sacred count.
Because the Haab has no leap-day correction, its 365-day count, the so-called vague year, drifts against the true 365.2422-day solar year by about one day every four years, so that Pop's seating cycled slowly through the real seasons over the span of a Calendar Round, taking roughly 1,507 years to complete a full circuit back to its original seasonal position. The day on which a year could begin, its Year Bearer, was restricted to one of four of the twenty Tzolk'in day names, spaced five apart because 365 divided by 20 leaves a remainder of 5; the specific set of four differed between the Classic period, when inscriptions show Ik, Manik, Eb and Kaban opening the year, and the Postclassic and colonial Yucatec system Diego de Landa recorded, in which Kan, Muluc, Ix and Kawak served as Year Bearers, a shift epigraphers attribute to a change in counting convention rather than to an error in either system.