whale tail

plural whale tails

1. slangfashionAn unintentional display of a thong above the waistband of trousers etc.

   So, next time you see a mom with a "whale tail" peeking out of her pants while she puts in a car seat, remember, "You can't judge a book by its cover."

   2007, Samantha Williams, “Dress to Impress Your Kids”, in The Daily News-Journal

2. slangautomotiveA kind of large automotive rear spoiler.

   the duck-tail spoiler was replaced with a whale tail for the US version of the Carrera.

   1997, Bruce Anderson, Porsche 911 Performance Handbook, page 16

3. Used other than figuratively or idiomatically: The tail of a whale.