Definition according to Mass Law but I'd imagine it's pretty much the same in most places.
Rape.—Sexual intercourse or unnatural sexual intercourse by a person with another person who is compelled to submit by force and against his will or by threat of bodily injury, or sexual intercourse or unnatural sexual intercourse with a child under sixteen years of age.
Aggravated Rape.—Sexual intercourse or unnatural sexual intercourse by a person with another person who is compelled to submit by force and against his will or by threat of bodily injury; and either such sexual intercourse or unnatural sexual intercourse results in or is committed with acts resulting in serious bodily injury, or is committed by a joint enterprise, or is committed during the commission or attempted commission of another offence.