Saint Patrick's Day, colloquially St. Paddy's Day or simply Paddy's Day, is an annual feast day which celebrates Saint Patrick, the most commonly recognised of the patron saints of Ireland, and is generally celebrated on 17th of March.
The day is a national holiday of Ireland: it is a bank holiday in Northern Ireland and a public holiday in the Republic of Ireland. It is also a public holiday in Montserrat. In Canada, United Kingdom, Australia, the United States, Argentina and New Zealand, it is widely celebrated but is not an official holiday.
Saint Patrick's Day is celebrated worldwide by those of Irish descent and increasingly by people of other ethnicities as well, notably in Argentina, Australia, New Zealand and North America. Celebrations are generally themed around all things Irish and, by association, the colour green. Both Christians and non-Christians celebrate the secular version of the holiday by wearing green, eating Irish food and/or green foods, imbibing Irish drink and attending parades, which have a particularly long history in the United States and in Canada.
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, and 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". (From: Wikipedia, license: CCA-SA)