I am not satisfied with most definitions of science I've seen so far, either essentialist or enumerative. I think the "social" definition below is much better:
1. Science is what scientists do [1].
It may not be very satisfying, but neither is it as glib as it first appears. Still, I believe it needs some precisions: obviously, not everything scientists do is science. This applies in private life (some scientists are atheists and others are deeply religious) but also to public attitudes: Johannes Stark was an authentic Nazi, but this does not prevent us from studying the Stark effect. Conversely, his scientific achievements do not render Nazism respectable. Then:
