Means really sexy or hot, or can also be used after a comment to define something sexy.
person one: "hey she is so hot man what u think"
person two: "omg man she is fuckin rawrrrr"
girlfriend on phone tired: "uuuuhhhh yeahhhh" (sexual noises)
boyfriend on phone: "rawrrr"
girlfriend on phone: "rawrrr"
girlfriend: "how about we do it on the pool table tonight"