The holiday season directly preceding X-mas.
This generally begins sometime after Black Friday/Cyber Monday when you are forced to attend the first Christmas Party of the season. It doesn't end until Christmas Day.
It encompasses all the crap that you have to do in order to prepare for X-mas: shopping, cooking, office parties, visiting your in-laws, etc.
I got us a bottle of wine for W-mas. Let's have a taste before we head back to the mall.
Dude, is that the new iPhone?
Yeah, my mom let me have it early. Happy W-mas to me!