It is a term most commonly used in pornography. It is also referred to as Internal Ejacualtion. In anal cream pie's the male will usually plunge deeper into the anus and stay there until they're through cumming. Then they will slide there penis out slowly as to help the cum flow out of the anus. The female will sometimes squat or probe with their fingers to help gravity move the sperm. In vaginal cream pie's the guy will cum inside the vagina and pulls out their dick slowly and the female will contract their lower stomach muscles to push out the cum. Vaginal cream pie's are far more common than anal cream pie's.
Let's just say she knows how to do one hell of a cream pie