What is 'pagan' here?

Everything before abrahamic religions is pagan or something more specific?

That's a somewhat sad question, because we hardly know. Not enough written record exists and "paganism" was increasingly outlawed during the past millenia to the point where we're out of people that had it handed down to them. The missionaries doing most of the recording were also the ones actively suppressing its survival. I'm aware of at least one revival movement that was active during the last 50 years, but the main instigator seems to have died without leaving a meaningful succession, and thus the preservation may very well have failed. Unless someone invents a time-machine a la Assassin Creed.

The etymology of the word 'pagan' originally meant hillbillies / dumb country people. It was a slur because the towns and cities adopted Christianity before the country people did. So, 'pagan' typically means the pre-Christian religions of Europe.

In the context of European Antiquity and Middle Ages - this means the original polytheist religions of the Romans, the Greeks, the Slavs, the Celts, the Germanic people...

Yes, from the context of Abrahamic religion and the cultures descended from it, all religions and cultures which are not Abrahamic are by definition pagan.

by definition, yes