Someone into masochism gets sexual pleasure from being hurt: they are turned on by pain.
When you see the word masochism, think "pleasure from pain." Masochism is the opposite of sadism, which involves getting turned on by hurting people. Masochists are the ones that like getting hurt, though usually not seriously. Besides sex, people talk about masochism in other situations. If an employee keeps asking for more and more work, and seems to enjoy being stressed out and pushed around by a boss, other employees may see this as masochism.