Definition of Ember Days
In ecclesiastical law, those days which the ancient fathers called “quatuor tempora jejunii" are of great antiquity in the church. They are observed on Wednesday, Friday, and Saturday next after Quadragesima Sunday, or the first Sunday in Lent, after Whitsuntide, Holyrood Day, in September, and St. Lucy’s Day, about the middle of December. Our almanacs call the weeks in which they fall the “Ember Weeks,” and they are now chiefly noticed on account of the ordination of priests and deacons; because the canon appoints the Sundays next after the Ember weeks for the solemn times of ordination, though the bishops, if they please, may ordain on any Sunday or holiday.
That's the definition of Ember Days in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.