Mental Abuse can take place in many forms.
Dictionary.com says its: to speak insultingly, harshly, and unjustly to or harshly or coarsely insulting language.
Urban Dictionary (who I dont usually trust) says: The act of or the effects of mentally scaring a person. The effects are often long term.
Bad Girls Club had mental abuse in it. The mother basically degraded her youngest daughter all the time. The youngster was left wondering what she did wrong.