Cruelty is pleasure in causing suffering to other living things or even themselves. Sadism can also be related to this as it means someone really enjoying this. Cruel ways of causing suffering may involve violence.
For example, if a person is drowning and begging for help and another person is able to help with no cost or risk, but watches happily. Bertrand Russell said that "the [causing] of cruelty with a good conscience is a delight to moralists. That is why they invented Hell."