The Outbox is a virtual box that encompasses the part. It becomes visible when you select a part. In this example, the outbox is displayed as green edges on the corners around the part. The size of the outbox is dependent on the part's orientation.
Primitive, surrounded by a large outbox due to its orientation.
The Outbox is used, for example, to rotate the part, and in Simple Outbox Packing. For operations that orientate the part according to its outbox, orient the part to minimize the outbox, for best results.