HOLY DAY OF OBLIGATION
The Catechism of the Catholic Church explains holy days of obligation this way:
On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord's Day, the performance of the works of mercy, and the appropriate relaxation of mind and body.
Family needs or important social service can legitimately excuse from the obligation of Sunday rest.
The faithful should see to it that legitimate excuses do not lead to habits prejudicial to religion, family life, and health [CCC 2185].
Days of abstinence are
Ash Wednesday and all Fridays of Lent
All Catholics 14 years of age and older. No Meat (Canon 1252)
--Days of fast (and abstinence) are Ash Wednesday and Good Friday. All Catholics from the ages of 18 to 59. One full meal and two lighter meals allowed. (cf. Canon 1252)
All Fridays and all days of Lent are times of penance (1250).
--Abstention from food and drink (water and medicines excepted) for one (1) hour before receiving Communion; does not oblige elderly and the ill and those attending them (919)