I feel that evil is self-explanatory. But a very broad definition I would use in most contexts is committing unnecessarily inhumane, despicable actions against other living things for no justifiable reason, purely out of the selfish and completely negative kind of sadism and self-interest against the basic decency and needs of a society by hurting others or damaging the public good.

Spousal abusers, rapists, unprovoked murderers, those who abuse animals or kill them wantonly without need for food or to the need to keep their population numbers down, or for selling/privatizing economic enterprises when not necessary for personal financial kickback.

I think that prison abolition is a very noble goal, for example. But in the meantime, socialists will unfortunately have to plan ahead at least decades into the future for the construction of prisons to house people like rapists, murderers, human and endangered species traffickers, bourgeoisie, etc.