Yes, well, verifiable would be a start.
Reproducible would be another.
And visible in other than in fables and fiction would be another.
Not a definition so much.
More a definer.
Certainly, 'belief' has very little to do with it.
'Every fact is backed up by the entire universe.' -Washburn.
Astrology fails the 'fact' test.
So does 'crystal power', 'aura reading', and other para- and quasi-
scientific humdrums.
So does memetics, so far....
But this could end up in circles....