All Muslims who are able are required to make a pilgrimage to Mecca once in their life. This is called the "Hajj" (sometimes spelled "Haj").
Mecca is in Saudi Arabia. Supposedly, the Saudis are expecting 2.5 million people on the Hajj this year.
The exact date it starts is apparently dependent on some kind of heavenly sign (I could not get a good answer to this on Islamic sites). Muslims are supposed to get info from their local Mosque.
The general time frame is from about now through sometime in the first week of March. Given Islam's emphasis on celestial signs, it is possible that the new moon (tomorrow) officially starts the season.
A huge riot was started in Mecca a few years back during the Hajj. It was apparently planned (Iran?), and scared the Saudis a lot. (I know, easy to do...)
Perhaps some Freeper who knows can help out?
If I understand correctly, it's an annual religious festival in Mecca. Every Muslim is to make a pilgrimage to this festival at least once in their life. I thought the pilgrimage itself was called Hajj, but I could be mistaken. It is a big event in Saudi Arabia; a lot, hundreds of thousands of people, show up for this every year.