It is sexualised behaviour by the offender which causes the victim to feel uncomfortable or afraid.
Sexual assault is a crime.
It occurs when someone uses their power or authority over another person, or takes advantage of another persons trust or respect to involve them in sexual activity or force sexual activity upon them. Sexual assault does not have to involve physical violence. In some cases violence may be part of the assault however in many cases violence will not be used, rather psychological threats, verbal threats, tricks or bribes may be used to make another take part in sexual activity. Violence does not have to be used to make it a crime. Sexual assault is an abuse of power.