Saint Patrick's Day, or the Feast of Saint Patrick, is a cultural and religious celebration occurring annually on 17 March, the death date of the most commonly-recognized patron saint of Ireland, Saint Patrick (c. AD 385–461).
On St. Patrick's Day it is customary to wear shamrocks and/or green clothing or accessories (the "wearing of the green"). St Patrick is said to have used the shamrock, a three-leaved plant, to explain the Holy Trinity.