Ember days are no longer an obligation, but it is a definite added option to Lent or Advent. Ember days are four separate sets of three days within the same week. These days are Wednesday, Thursday and Friday.
On Ember days, one must not eat between meals and only eat meat for one meal. If an ember day falls on a Friday, do not eat meat at all.
Before Christianity came, Ember days were for pagan practices. It was abstaining and fasting for renewal. Catholic bishops tried not to take it over but have it adapted for Catholicism.
These days set apart for special prayer and fasting were considered especially suitable for the ordination of clergy. The Ember Days are known in Latin as the quattuor anni tempora (the "four seasons of the year"), or formerly as the jejunia quattuor temporum ("fasts of the four seasons").
The Ember Weeks—the weeks in which the Ember Days occur—are the weeks:
between the third and fourth Sundays of Advent (although the Common Worship lectionary of the Church of England places them in the week following the second Sunday in Advent);
between the first and second Sundays of Lent;
between Pentecost and Trinity Sunday; and
The week beginning on the Sunday after Holy Cross Day (September 14), the liturgical Third Week of September.