Quarter Days Definition:

The four days taken by custom to mark the quarters of the year. On these days, tenancies begin and end, and rents and other quarterly charges become due. In UK and Ireland the quarter days are: 25 March, 24 June, 29 September, and 25 December - or, Lady Day (the fest of the Annunciation), Midsummer Day, Michaelmas (the Feast of st. Michael), and Christmas Day.