In order to understand what it is, it is maybe easier to say what it is not.

it is not “Fairness” life isn’t fair, get over it. it isn’t “Mercy”, that is the domain of the merciful who often don’t exist, and it damned sure isn’t “Justice” because justice is a moving target.

One thing moral absolutes are not, and have nothing to do with, are Crime, and Punishment.

Lots of things are crimes, and they are not remotely immoral. Speeding on a long stretch of highway in the desert? Crime. Not immoral. Speaking your mind in Chicom country? Crime. not immoral. In fact a great deal of crime, and the laws that are aimed at controlling behavior, are not about immoral behavior at all, and as often as not the very law itself is immoral, because it is a theft; it’s a crime to carry a loaded firearm in Illinois except under the most stringent of circumstances, and that in and of itself is immoral, because it robs the individual of his or her right to defend his or her person.

No, to discuss justice or mercy or crime or punishment or fairness in the same breath as moral absolutes is to grossly misunderstand the meaning of moral absolute, and we can always return to the basic moral absolute of theft, because a lot of other moral absolutes are based on it. Kill someone? you are stealing their right to live. Rape someone? Stealing from them their ability to determine what happens to their own body.
A moral absolute is something that is wrong no matter who does it nor who it is done to. Stealing a loaf of bread is stealing a loaf of bread. Doesn’t matter if yopu steal it from a pauper or a millionaire, doesn’t matter if you are in need or just like stealing, the only consideration is the theft itself and that theft is always wrong. There is no circumstance under which it is not. nobody deserves to take someone else’s property without consideration, period. And from this moral absolute springs all others.