On this tab, you can define which forums will be included in the currently edited index.

 

Forum indexes can be defined by adding forums as allowed or excluded. The dialogs for making the settings can be accessed using the Add allowed forums and Add excluded forums links.

 
More resources can be found at:

 

•Developer's Guide -> Modules -> Smart search -> Overview

•Developer's Guide -> Modules -> Smart search -> Managing indexes -> Defining forums index content