The difference between sexual assault and rape is that rape is a subset of sexual assault. “Sexual assault” is not a specific defined crime, but includes a wide variety of behaviors.
Rape is the crime of having sexual intercourse with an unwilling participant of one that does not possess the legal capacity to give consent. Obviously, a stranger who physically threatens a woman if she will not have sex with him is raping her, but “date rape” is when an acquaintance forces sexual intercourse on a woman who objects. The fact that she may have voluntarily been with him, as on a date, is no defense when she says “no.”
The legal capacity to give consent comes into play when a woman is unable to say “no,” for one reason or another. We occasionally hear about a dentist raping a patient who is unconscious. It is rape because she cannot give consent, whether she would do so or not while awake. Having sex with a woman who is too drunk or high on drugs to know what she is doing is also rape, in that she does not have the capacity to give consent.
Statutory rape is based on the same principle. The law takes the position that a female under a certain age is not mature enough to make such a decision, so sexual intercourse with a female under a certain age, frequently 16, but in some states as low as 14, is the crime of statutory rape. It is so because the statutes dictate that a female of that age cannot give consent.
Sexual assault, on the other hand, includes much more than rape, although the lack of consent or legal capacity to give consent is the common thread. Molesting a child is sexual assault, even though there may be no intercourse at all. A child cannot give consent, so fondling (sexually), exposing a child to pornography, exposing oneself to a child, or taking pornographic photographs of a child are all forms of sexual assault.
Exposing oneself to an adult is also a form of sexual assault, as are attempted rape, making obscene telephone calls, and voyeurism. Every so often we hear about someone who looks in women’s windows, or has a peephole into a shower of toilet. These people are committing forms of sexual assault. Unwanted touching or sexual comments can certainly be considered sexual assault, as any form of sexual harassment could be.
Victims of sexual assault need help, starting with needing someone they tell to believe them. If Jane tells you that she has been sexually assaulted by Joe, the last thing she needs is for you to say “Oh, I can’t believe Joe would do that.” If she is telling you this, she needs you to listen, believe her, and not blame or judge her. It is difficult enough to tell someone, and she trusts you to be receptive. The Washington Office of Crime Victims Advocacy has some excellent information if you or a loved one has suffered from sexual assault.