A Work Order is a special type of infinitely repeatable quest given by the crafting masters. Their main purpose is to provide a way of increasing the level of a player's crafting skill. The player gains a small amount of experience per craft and per repeat, and will also be given a randomized ingredient or design as a reward for successfully completing the Work Order.
If you fail to make the required number of items for the Work Order, you will need to press (J) to open your Quests window and go to the Work Order Tab. From there you can click on the work order and select Abandon.