Traditional (and originally), it is the Celtic Holiday Samhian or Late Harvest , and represents the Celtic New Year. So being a half drop Irish, and having a good pint of Celtic blood in me, I think it would be a lovely day for a Guinness!
Happy New Year!
T.S. No, I did not Wiki this...I'm here all week!
T.T.S. TS stands for Toe.Spit, which is a spoonerism of Post Script...again, I'm here all week!