From the Office for Civil Rights:
Title IX requires schools to take steps to prevent and remedy two forms of sex-based harassment: sexual harassment (including sexual violence) and gender-based harassment Sexual harassment is unwelcome conduct of a sexual nature. It includes unwelcome sexual advances, requests for sexual favors, and other verbal, nonverbal, or physical conduct of a sexual nature. Sexual violence is a form of sexual harassment. Sexual violence, as OCR uses the term, refers to physical sexual acts perpetrated against a person’s will or where a person is incapable of giving consent. A number of different acts fall into the category of sexual violence, including rape, sexual assault, sexual battery, sexual abuse, and sexual coercion.
Title IX also prohibits gender-based harassment, which is unwelcome conduct based on a student’s sex, harassing conduct based on a student’s failure to conform to sex stereotypes.
Sex-based harassment can be carried out by school employees, other students, and third parties. All students can experience sex-based harassment, including male and female students, LGBT students, students with disabilities, and students of different races, national origins, and ages. Title IX protects all students from sex-based harassment, regardless of the sex of the parties, including when they are members of the same sex.