One of the three Maya calendars, and the one which corresponds most closely to ours in length. The haab is also known as the "Vague Year" by archaeologists, since it is 365 days in length, or about a quarter day short of the actual solar year.
The haab' is a 365-day calendar that approximates the length of the seasonal year (which is 365.2422 days in length). Dates in the haab' consist of a coefficient (or number) ranging from 0 to 19 or from 1 to 20 and a glyph referring to one of the 18 months of the haab'. Each of the months was 20 days in length, with a final 5-day period at the end of the year called Wayeb'.