"Wednesday, Friday, and Saturday after Quadragesima Sunday (the first Sunday of Lent) are known as "Lenten Embertide," which, depending on the date of Easter, can come as early as February 11, but which is seen as associated with the season of Spring (March, April, May). Liturgically, the lessons for the Wednesday and Saturday Masses focus on the Commandments given to Moses by God, and on the promises to those who keep them well, all ending with the story of the three lads saved by an angel from Nabuchodonosor's furnace, as is so for all but Whit Embertide.
The Gospel readings speak of Our Lord discoursing on the sign of Jonas, and how exorcised spirits can return (Matthew 12:38-50), healing the paralytic (John 5:1-15), and the Transfiguration (Matthew 17:1-9)." These three days are traditionally days of fasting and abstinence. You can read the rest on Fisheaters.com