i think there are two tracks.
one track is to self: so, sin to, and or of, self is something you do that results in having to repair or restore goodness.
another track is to those outside of self: so, in this case i view sin as something that harms another living organism and requires repair to others and/or environment. yes... this does mean that i sin when i kill a spider in my house, which is why the right thing to do is capture it and toss it outside.
i don't buy into the god, heaven, hell movement, however, it remains just as important not to sin in my view -- for the simple reason that when i die i'll accept that i did the best that was humanly possible given the tools i had.