Cutting through a forest of controversy and opposing opinions is a revelatory experience. I have not much to add to the following answer to what is moral progress.

Waking Up with Sam Harris – #48 What is Moral Progress

Sam Harris:

If you picture our world much better than it is, in moral terms, what do you picture there? What are the most important ways our morality — just speaking globally, collectively — can improve? What does the world look like at that moment?

Peter Singer:

Well, the world takes much greater notice of suffering and misery, wherever it is happening, and to whoever it's happening to. When I say 'whoever', I don't only mean human beings, I mean non-human animals as well. When we are talking about human beings, whether they are close to us, whether they are, for example, fellow Americans, whether they are people living in distant countries who we'll never meet. And still, we have the view that it's bad that there should be avoidable suffering and for that matter avoidable premature death. So, I would see this as a world in which we use our resources more effectively than we are now, in order to assist people in extreme poverty, to help them to live better lives, to help them to have enough to eat, adequate healthcare, education for their children, and opportunities by hard work and diligence to get out of poverty. Because I think that global poverty is one major source of avoidable misery.

It would also be a world, as I was saying, in which we extend our concern to non-human animals, so we would not have a world in which — as we currently do — something like animals are raised and killed for food each year, the vast majority of them living miserable lives confined in factory farms, intensive farms, often crowded, so they don't have room to walk around. And the whole system being, in any case, a net waste of food, causing net food loss, because we have to feed these animals grain which we could otherwise eat directly ourselves. […] So essentially that's how I would see moral progress: As reducing avoidable misery and suffering and, where possible, making people happier, more fulfilled, more satisfied with the life they're living.

I would even consider this the definition of progress in general.