Before Vatican II, every Friday (Lent or not) was a day of abstinence from meat. But today, in most countries, meatless Fridays are only during Lent. This includes the United States. The Catholic Church does still recommend that some sort of penance or work of mercy be performed for the Fridays outside of Lent. This is to show reverence for the day of the week that Jesus died for our sins.
As far as Abstinence and Fasting during Lent see: http://www.catholicadventure.com/2010/02/fast-facts-about-lent.html
As far as Abstinence and Fasting during Lent see: http://www.catholicadventure.com/2010/02/fast-facts-about-lent.html