Leatherworking is one of the primary professions. Your character can only have 2 primary professions at any time.
The Leatherworking profession allows players to utilize the Leather gathered through the Skinning profession to create a variety of items, including cloaks, leather and mail armors, armor kits, quivers, and ammo pouches. The armor produced by Leatherworking is chiefly of use to the leather- and mail-wearing classes: the Druid, Hunter, Shaman, and Rogue.
More information can be found on WoWWiki.[]