Recipe

Crafting Recipes are the means to how crafters learn new items that can craft with their skill. When you first start crafting you have access to a smaller list of items that you can craft and require recipes to expand the item list.

Source
When you complete a Crafting orders in any skill you receive a random recipe for the skill you completed the crafting order for. You may end up getting a recipe you already have which are often sold by players to those who do not want to do Crafting orders to find a specific recipe.

Recipes by skill
When you first start crafting in any skill the items available. The following lists show which recipes are available for each skill.