sheath line means: Sheath Line is a sheath line dress that fits close to the body. It also ends at the knee, or below like other cocktail dresses. You can think of Audrey Hepburn and Jackie Kennedy Onassis in “Breakfast at Tiffanys”. The style can be described as simple, with a lot of block colours and no embellishments — perfect for Little Black Dresses. (in Fashion Dictionary)