One of the books I’ve been reading recently is Medieval Europe: A Short History by Hollister. He uses, quite often, the abbreviation “f.” or “ff.”, for example:
The Golden Age of the Abbasids: 750 ff.
I wasn’t sure what the abbreviation meant, so I dutifully looked it up. It apparently means, simply, “and the following (pages, verses, years, etc.)”.
(The abbreviation can also stand for “fortissimo”, meaning “in a very loud manner”, but I’m fairly confident that that isn’t the meaning Hollister had in mind!)
One of the f’s could stand for folio. But I’m not sure about the other. Maybe just ‘following’ indeed?
I think it is a perfect synonym for “et seq.” meaning “and the following (pages).”