Abuse is a general term for the treatment of someone that causes some kind of harm (to the abused person, to the abusers themselves, or to someone else) or is unlawful or wrongful. Physical abuse is abuse involving contact intended to cause pain, injury, or other physical suffering or harm. Psychological abuse refers to the humiliation or intimidation of another person, but is also used to refer to the long-term effects of emotional shock.
Psychological abuse can take the form of physical intimidation, controlling through scare tactics and oppression. It is often associated with situations of power imbalance, such perhaps as the situations of abusive relationships and child abuse; however, it can also take place on larger scales, such as Group psychological abuse, racial oppression and bigotry. A more "mild" case might be that of workplace abuse. Workplace abuse is a large cause of workplace-related stress, which in turn is strong cause of illness, both physical and mental (see battered woman syndrome).
There need not be an agitator for psychological abuse to occur — one can undergo self-abuse, as in the case of someone who is a depressive, or self-mutilation.
Any situation in which the repeated and extreme impact of a situation affects a person's emotional and rational thinking, in such a way as to adversely impact their later lives, could be termed as psychological abuse at some level.