Ahimsa

Ahimsa is usually translated straight-up as 'non-violence,' which has a pretty obvious literal meaning, but I'm not going to approach that or the definition-arguments (ie, the monk/snake story or the Bhagavad Gita taking place on a battlefield).

Rather, I'll speak to the subtler elements that have struck me in the past (not to pun, there). One is that violence doesn't necessarily mean physical violence, of course, but includes the whole gamut of mental, emotional, and verbal violence as well. Thus, the parallel interpretation of the Christian commandment, 'Thou shall not kill,' that includes insulting someone as a sinful action - in a sense, an insult is injurious, as much or more as physically hitting the person is. Following this thread to a different point, in terms of one's own health, violence to others is often hurtful to the self as well; if one has a developed conscious, there will be guilt, or that violence will be reflected back upon the inflicter (insults flung back and forth, resentment and bitterness ruining relationships, say).

And, following that thread a little bit further, as much as the yamas are directed externally, one should also note that the principle of ahimsa can apply internally as well - obviously, banging one's head into a wall probably falls under the umbrella of violence-to-self, but less obviously is second-guessing, self-pitying, baseless anger towards the self, and other negative things of that ilk.

Long and short of it (here's the important part), developing ahimsa in these senses means working on becoming more aware, considerate, and empathetic towards the effects of one's actions on others (and Self), for both healthy relationships, and one's own health as well.