NRATH is an acronym for Not Really All That Hot. Pronounced "n - wrath". Used to describe a girl that is decent looking, but not really all that hot. Perhaps someone described a girl as really, really fine, then you saw her and thought to yourself, "meh, she's not really all that hot." Women can also use this in describing men's hotness.

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