A Ceilidh (pronounced "Kay-lay", emphasis on 1st syllable) derives from the Gaelic word meaning a visit and originally meant just that (and still does in Gaelic). It can also mean a house party, a concert or more usually an evening of informal Scottish traditional dancing to informal music.
About St. Andrew's Day
St. Andrew is the patron saint of Scotland and the official St. Andrew's Day is on November 30th. Andrew, the Apostle, was added to the communion of saints of the Pictish Church in the 8th century.