If you call a person, a remark, or a decision callous, you mean they do not care that other people are hurting. They look at pain and stay cold. It is a strong, judging word, a little formal; in easy talk people might say cold or heartless instead. You hear it about bosses, rules, jokes that land on someone already down. Though actually, the word began as a picture of thick, hard skin that no longer feels much. That skin sense still exists, but when we talk about people we almost always mean the heart, not the hands.