two days after the Ides of March
In america this Holiday is a.k.a. the "Wearin o' the Green" day.
It's a day for parades that celebrate Ireland or being of Irish heritage.
Some pubs dye ther beer or anything else green with food coloring. It is too bad because Certain foods, like eggs, when dyed green, look incredibly puke-inducing.
see cinco de mayo
It is the date that Saint Patrick died. Saint Patrick is the man who is said to have introduced the catholic religion to Ireland. He tried to explain "the trinity" (3 people in the one god) with a three leafed plant called a shamrock. Hence the shamrock has significance for the day. Originally the day was important only in Ireland but because of the large numbers of Irish people who emigrated abroad and the colorfulness of the celebration the tradition spread around the world.