When we abstain from eating meat what does this include?

To abstain from eating meat (such as Fridays), what all does this include? Just red meat? Chicken? Eggs? Or is it abstaining from a certain desire?

III. 1. The law of abstinence forbids the use of meat, but not of eggs, the products of milk or condiments made of animal fat. Paenitemini

“The trouble is that this explanation–at least in its English translation–is not as clear as one would like. It does not, for example, mention the exception of fish and other seafood from the law of abstinence, and this is universally acknowledged as an exception. The reason the exception is not mentioned is that it is implicit in the original Latin of the text, which reads:

Abstinentiae lex vetat carne vesei, non autem ovis, lacticiniis et quibuslibet condimentis etiam ex adipe animalium [III:1].

The word for “meat” in the original is carnis (here inflected in the ablative as carne), which does not correspond exactly in meaning to the English word “meat.” In contemporary English, “meat” tends to mean the flesh of any animal, whether it is a mammal, a bird, a fish, or what have you. But as used here, carnis refers only to the flesh of mammals and birds. It does not include the flesh of fish (or, for that matter, of reptiles, amphibians, or insects).
Another possible exception to the rule may be found by comparing the norm in Paenitemini to the original regulation in the 1917 Code of Canon Law, which held:

The law of abstinence prohibits meat and soups made from meat but not of eggs, milks, and also whatever condiments are derived from animal fat [CIC(1917) 1250].

Since the 1917 law included an exclusion of soups using meat but the 1966 norm does not, in the common opinion of canonists today appears to be that soups using meat no longer violate the law of abstinence. (A few Lents ago, I did an extensive check on this.) Notice that the rest of the sequence (meat, eggs, milk products, condiments) is entirely undisturbed, suggesting that soup was intentionally dropped.”

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