First, what it is not. It is not merely those things I dislike, those things which make me angry or which I find disgusting. I may dislike immoral things and find them disgusting, but that is not sufficient to make them immoral.
Morality is that system of evolved instincts and evolved social norms which allow people to live together in societies, and so to benefit from living in societies. Nothing more, nothing less. That is moral which allows the largest number of people to participate in society without abridging the ability of the individual to reap full benefit from being a member of the society.
That which makes the society one is part of larger is a moral good, so long as it does not do so to the detriment of current members of the society or those who are joining the society as a result of the enlargement.
Morality serves first to allow us to live with and benefit from our immediate social circle, then the next layer of society, and the next, all the way out to humanity as a whole. Therefore it is most moral to benefit your immediate social circle, then the next layer of society, and so on, so long as benefiting one social layer does not harm other members of the wider society.
Morality is that which allows people to live together, and so applies most immediately (only?) to beings which can be classified as people. That is, conscious, sentient social beings. It applies to humans by default, as we cannot meaningfully distinguish humans who meet the criteria for personhood from that subset, if any, who do not.
Morality concerns the well-being and thriving of people as individuals and as communities.
This is not a fallacious Appeal to Nature. That is, I am not saying that this is how morality has developed naturally, therefore this is what it should be. Rather, I am saying that this is what morality is. Morality doesn't have its own ontology, so that it can be shaped by naturalistic (or any other) framework. Morality simply is the system of evolved instincts and evolved social norms which allows people to live together.
Some may object that this robs morality of its moral force, reducing it from something transcendent to something pragmatic. I would argue that it cannot be reduced to pragmatism, because that is simply what it is. That seeing it for what it is may rob it of some of its force is unfortunate, but irrelevant to what it is.
I realize that the description I have given of morality neatly matches by own moral biases. It may be that my moral instincts are perfectly informed by the reality of the nature of morality, in which case I can carry on secure in the conviction that my moral compass is true. But I have to acknowledge that it is more likely that my description of morality has been influenced and shaped by my biases, and so needs review and refinement by people who don't share my particular set of moral assumptions.