Lá Fhéile Pádraig = “the Day of the Festival of Patrick” — Saint Patrick is the patron saint of Ireland, which is where the wearing of the green comes into it. (Also, green beer. ugh.)
Patrick was a Roman British man who was enslaved and taken to Ireland, where he found God. He escaped Ireland and became a priest and later went back to Ireland to convert as many as possible to Christianity. This is actually where the idea of St. Patrick “driving all the snakes out of Ireland” comes from. He was determined to either convert or remove every pagan in Ireland. In fact, Ireland has never had any real snakes. 🙂
Enjoy your carousing!
Cheers,
t.