Sexual violence refers to abusive sexual contact, making a person engage in a sexual act without consent, and attempted or completed sex acts with a person who is unable to consent to sexual contact.
It can take many forms, including any unintended or non-consensual sexual act, sexual harassment, and violent acts. A person may be unable to consent due to their disability (however, having a disability does not mean a person is automatically unable to consent to voluntary sexual conduct). Other reasons a person may be unable to consent include that the person is asleep, unconscious, ill, under pressure, or under the influence of drugs or alcohol.
Source:
United Nations Population Fund (UNFPA), UN Women, World Health Organization (WHO), United Nations Development Programme (UNDP), and United Nations Office on Drugs and Crime (UNODC), Essential Services for Women and Girls Subject to Violence (Module 1) 10 (2015), http://www.unfpa.org/publications/essential-services-package-women-and-girls-subject-violence