Alignments are always a touchy subject, as EVERYONE has different interpretations about them. You should note though that players can have any kind of view, but the only one that matters is the dm's
This. I learned this, in spades, when I started running Vampire: the Masquerade, where there are mechanical penalties for evil behavior. By the end of the second session, I determined that there could only be one definition of good and evil and that only the GM could make that call. I don't care what you believe about various political/religious/philosophic questions IRL, it's got to be the GM. That carried over to D&D.
The good news for my players is that I allow evil characters; as long as you aren't disruptive, I don't care. Also, there are no mechanical penalties for alignments in 98%+ of cases. You can act however you want, but I determine how that's described. Also, I'm more than willing to tell you, up front, whether I consider an act good, evil, lawful, or chaotic.
Here's my high-level:
Good: Willing to actively help someone else out, at cost to yourself.
Evil: Willing to actively damage someone else, for relatively minor gain.
Morally Neutral: Will help others if there is little/no personal cost. Unwilling to inflict significant harm on others except under duress.
Lawful: Tendency to think in terms of groups, patterns, etc. This tends to lead to codified laws, formal honor, and other structured relation to the world. Does
not require adherence to all laws, just a desire to organize things.
Chaotic: Tendency to think in terms of individuals, specific circumstances, etc. This tend to lead to disregard for laws, reliance on judgement, and other adaptable relation to the world. Does
not require antagonism, just a desire to be free.
Ethically Neutral: Favors neither extreme. Could be actively balanced between the two extremes. More likely to think you're doing too much navel-gazing.
Personally, I hate when people look at Chaotic Neutral as either "crazy" or "get away with anything". Mental health is not an alignment. All alignments have to be meaningful. Chaotic Neutral is an individualistic person who rarely acts with either charity of cruelty.