A boat neck, also called a bateau neck or Sabrina neckline, is a wide, high neckline that runs horizontally, front and back, almost to the shoulder points, across the collarbone. For no real reason other than one sounds casual and the other sounds dressy, people are more likely to use boat neckline for casual tops and bateau neckline for cocktail and formal gowns. The Sabrina neckline usually has a little bow on each shoulder where they connect.
The A to Z of Fashion Writing 