https://www.gamespot.com/articles/fortnite-battle-royale-characters-backs-are-now-cu/1100-6456923/

Epic Games has been adding a bunch of new content to Fortnite, especially as the game's popularity has continued to rise. In the Season 3 Battle Pass for the Battle Royale mode, for example, the developer is releasing some new cosmetic items, such as emotes, loading screens, outfits--and Back Blings.

You read that right: Epic has added a new customization option for your Hero that modifies the appearance of its back. Basically, anything that a character holds on its back is now part of this option, so you'll be able to change out previously permanent characteristics like the Love Ranger's wings or the Knights' shields.