when two people are laying down together, typically a couple with one of them on their backs, the other has one of their legs reached over the other's body. Such a case would be a man laying down, with one of his girl's legs going across his body while the other is parellel with his own... such a position typically brings the couple's faces together and is ideal for cuddling, kissing, and generally intimate.

the whale tail is the shape formed when a g-string rides up high over a womans trousers