One may not even touch the other person physically. Yet one may harm the other person more severely emotionally or mentally. This is called psychological violence.
Verbal aggression is one of the main way through which Psychological abuse happens or is initiated.
Threats, taunts, ignoring, insults, criticism, mockery, teasing, ridiculing, criticizing, blackmailing are all the examples of psychological violence.
The not so visible form is brain washing, advertising wrong values, imposing one way of life or beliefs, etc.