The Ember Days are Wednesday, Friday and Saturday found at four times of the year in connection with the four seasons. At this time of year, nearing Winter, the Ember Days come after the Third Sunday of Advent. These days are also called the "Ember Fasts." Traditionally Ordinations take place during the Ember Days.
An advantage of the practice of daily Mass or Low Mass is that one benefits from the extra Scripture readings that are available on these days, here in connection with Advent and Christmas:
Wednesday: Isaiah 2:2-5, Isaiah 7:10-15, Luke 1:26-38
Friday (today): Isaiah 11:1-5, Luke 1:37-47
Saturday: Isaiah 19:20-22, 2 Thessalonians 2:1-8, Luke 3:1-6
(optional additional lessons: Isaiah 35:1-7, Isaiah 40:9-11, Isaiah 45:1-8,
Daniel 3:47-51, Daniel 3:52-56)
Fasting is the traditional practice on these days. Nowadays, where fasting is not the usual practice, it may be encouraged as an aid according to one's own devotional practice.