Prior to Vatican II abstinence from what was called “flesh meat” was required in all Fridays. I have heard several descriptions of what flesh meat is but is always includes beef, pork, mutton, and fowl. for this question, that matters not.
Catholics in the US are required to perform some penitential act on Friday’s year round. the US bishops recommend abstinence from meat but it is no longer required. As this is a devotion (sort of) there are no hard and fast rules.
Traditionally, there are several levels of abstinence. The least onerous would be the one listed above. Next would be that of all flesh including sea food. Next would include the above and include dairy products. Finally, you could go the John the Baptist route and limit yourself to honey and locusts. You select your self imposed penance, just be consistent and do not do something that will cause you actual bodily harm.
As an aside, I have been limiting myself to fish and/or veggies on Fridays since I came back to the Church. I also (usually) fast on Friday.
Patrick