First of all, The Hamster King has it right: morality is meaningless outside of a social context. That doesn’t mean that you yourself have no morality when you are alone and unwitnessed, because you (the generic you, not any specific individual) have morality acquired from your time within a society, which you may or may not have modified with your own thoughts over time.
So morality exists only within a social context. And the definition is pretty straightforward: morality is that behavior on the part of its individuals which allows the society to exist and flourish.
This splits into two parts. The first is those behaviors agreed upon by virtually every society that we’re aware of: don’t kill, don’t lie, don’t steal. There’s one other that is a bit more problematical that I’ll get into a bit later on.
The second part of morality is those things unique to an individual society: religious observances, shibboleths, marital rules, dietary restrictions, membership rituals such as circumcision, etc. They’re things that, regardless of why people believe them important, primarily serve the function of distinguishing this society from others and, not incidently, a tool for the powerful to establish or acquire and retain power over citizens of that society. As far as I personally am concerned, this portion of morality is largely as Rand Rover described in his opening paragraph, especially in a multi-cultural society like the US. As long as one is willing to accept the shunning that some portions of society may inflict in response, one can break any of these rules to their heart’s content, insofar as they don’t violate the first part of morality.
So back to the first part. We have three very straightforward rules for individuals: don’t kill, don’t lie, and don’t steal. (I say individuals, because as a whole, the society as embodied by its government/priesthood, may kill and/or steal <i.e. tax> without necessarily being considered immoral. In recent years, modern societies have started holding their officials to some of the same standards to which they hold individuals - not a bad idea in my eyes, at least in some cases)
But there’s a fourth universal rule of morality that makes everything a lot more complicated. It boils down to: don’t make the people around you miserable. Or as the SDMB says it, don’t be a jerk. Unfortunately, this covers a lot of extremely nebulous ground, from torture to just being a pain in the arse.
But these rules are not just “made up” by the individuals, Rand Rover. Every known society believes in them, and the vast majority of individuals within those societies believe in them. What screws it up is balancing competing claims, both of morality versus individual self-interest, and of one piece of morality versus another. For example, we tend to agree that killing someone who is trying to kill you is OK, but deciding the precise point at which it is definite that that someone is trying to kill you is often not clear-cut. It’s not that the rule varies, but the assessment of the situation varies. That’s why, in our society, we have courts, not only for criminal cases, but for civil cases as well. Every other society that I’m aware of has had some similar institutionalized form of arbitration, often as simple as the ruler making the judgment.
It may seem like hairsplitting to you, Rand Rover, but to me it’s the essence of human societies. The rules tend to be close to universal and absolute (except for the “don’t be a jerk” rule, which is absolute in essence but often exceedingly difficult to determine in practice), but situations themselves are rarely straightforward and clear-cut, and the various rules at times weigh against one another. This does not, as far as I am concerned, invalidate these rules or absolve the individual from doing one’s best to behave morally.