Catholics abstain from meat on Fridays because Jesus died for our sins on Good Friday, and it's a way of mourning and doing penance for the sins for which Christ died. (By the same token, Sunday-the day on which Christ rose for our salvation-is an especially appropriate day to rejoice.) It's meat because it should be a sacrifice - giving up something that we enjoy and in the past meat was a luxury of people - so they are giving up a luxury. Also meat/flesh is a good symbol for giving up things of the flesh to enhance the spirit.
In the US Catholics are only required to abstain from meat on Fridays during Lent (the 40-some days before Easter). Catholics in other parts of the world abstain from meat on every Friday of the year.
at 11:21 AM on Feb. 24, 2009