Good Friday is a day of Fast and Abstinence. Fasting means adults from 18 up to the age of 59 can have only one full meal and two light meals with no food between meals. Of course, those with health concerns are excused. Abstinence means no meat for anyone over 14 years old.
The Good Friday fast and abstinence is different from Lent. This is called the Paschal Fast and is a joyful anticipation before Easter. It is like being too excited to eat before your wedding, not just mourning the death of Jesus. We look forward to the joy of resurrection. While the requirement is only for Good Friday you are invited to extend it to include Holy Saturday.