Saint Patrick's Day (Irish: Lá ’le Pádraig or Lá Fhéile Pádraig), colloquially St. Paddy's Day or simply Paddy's Day, is an annual feast day which celebrates Saint Patrick (circa AD 385–461), one of the patron saints of Ireland, and is generally celebrated on March 17.
It's celebrated because...As well as being a celebration of Irish culture, Saint Patrick's Day is a Christian festival celebrated in the Catholic Church, the Church of Ireland, and some other denominations. The day almost always falls in the season of Lent. Some bishops will grant an indult, or release, from the Friday no-meat observance when St. Patrick's Day falls on a Friday; this is sometimes colloquially known as a "corned-beef indult". When 17 March falls on a Sunday, church calendars (though rarely secular ones) move Saint Patrick's Day to the following Monday—and when the 17th falls during Holy Week (very rarely), the observance will be moved to the next available date or, exceptionally, before holy week.