What does Back Door Santa mean?

Back Door Santa meaning in Urban Dictionary

Preferably on xmas eve, while having sexual intercourse doggy design with your girl friend, in the same way your about to climax you sneakily fall it into the woman ass. When she converts round in shock and horror you grab and ejaculate all-around the woman face yelling 'Ho,ho, ho' making her rosy cheeked with a white beard the same as Santa Claus.