Broadly speaking, AOVs in RIS fall into three main categories: built-in, integrator (global), custom, and light path expressions.
For users interested in what is typically referred to as "render passes" for compositing a beauty image, look at the page on light path expressions (LPE).
The built-in AOVs display mostly geometric information pertaining to points on the visible surfaces seen by the camera. These values are automatically generated by the renderer and are available as AOVs regardless of the active integrator. Here is the current list of available builtin-ins: