a self-conscious emotion associated with feelings of worthlessness or humiliation

Shame is an emotion. Shame is rooted in a social or cultural environment. Some people feel shame when some of the rules (that are accepted by the respective society) have been broken. A person can feel ashamed because he or she has thought or done something no one else knows about. Children are often told to be ashamed of something, because they sometimes have trouble telling cause and effect apart. When they grow up, they can better tell the two apart. At that stage, the feeling of guilt becomes stronger.