Its a part of fasting. Aside from giving up a quantity of food in fasting, you also give up luxurious foods (meat, eggs, cheese, etc.)
"And the disiples of John and the Pharisees used to fast; and they come and say to him: Why do the disciples of John and of the Pharisees fast; but thy disciples do not fast? And Jesus saith to them: Can the children of the marriage fast, as long as the bridegroom is with them? As long as they have the bridegroom with them, they cannot fast. But the days will come when the bridegroom shall be taken away from them; and then they shall fast in those days." (St. Mark 2.18-20)
I asked what the repercussions were to eating meat.