If you have ever implemented things like viewport culling or picking, you may have encountered the Axis-Aligned Bounding Box (AABB). This bounding volume has two vectors, one containing the minimum corner (x, y, z) and once containing the maximum corner (x, y, z) of the box. Although it is fast to perform different intersection tests, etc. with this volume, it is quite inaccurate in many cases.
To describe the world your objects will interact with in the physics simulation, Oriented Bounding Boxes (OBB) will be used instead. By combining several of these Oriented Bounding Boxes, complex-enough worlds can be built for the purpose of this book. Figure 6.8 shows an image comparing the AABB and the OBB in two dimensions: