Global Texture AOVs apply a texture to the entire scene including or excluding the environment (figure 1). Global Texture AOVs are rendered as info AOVs, which means that the info AOV settings are applied to them as well. You can overwrite the alpha channel with your own texture, or use the default behavior which is equal to the alpha channel of the other info AOVs.
Figure 1: Accessing the Global Texture AOVs in an Octane Render Target node