Fasting is the act of doing with less. In the Catholic Church, those ages 18 - 59 must fast on Ash Wednesday and Good Friday (Canon 97). On such days, those fasting may eat one full meal ...
Good Friday is just one part of the larger Holy Week that proceeds, with the conclusion marking the end of a 40-day fast ...
As this is a day of mourning, Catholics should, if possible, refrain from work and participate in the liturgy. The Church also teaches that Good Friday is a day of fasting and abstinence.