The Long Count is part of the Mayan Calendar
notation. It is determined by the number of days that have passed since the beginning of the current Mayan era
, sometime in September, 3114 BC, although there is some debate
on the actual date.
There are five units in the long count: Bak'tun, K'atun, Tun, Winal, and K'in. They are as follows:
1 Bak'tun = 20 K'atun = 144,000 days
1 K'atun = 20 Tun = 7,200 days
1 Tun = 18 Winal = 360 days
1 Winal = 20 K'in = 20 days
1 K'in = 1 day
For reference, today would be labeled as 12 Bak'tun, 19 K'atun, 9 Tun, 12 Winal, 1 K'in in Long Count (using 584,285 correlation) by the Mayans. In modern notation, these numbers are given as a string of numbers, which looks like 188.8.131.52.1.
"The Mayan Calendar", http://www.halfmoon.org/calfork.html
"Gregorian-Mayan Date", http://www.pauahtun.org/cgi-bin/gregmaya.py