On this tab, you can choose which sites will be indexed by the currently edited index. You can choose more than one site, which results in a multi-site index.

 

Please note: You need to rebuild the index in order for the changes made on this tab to take effect.

 
More resources can be found at Developer's Guide -> Modules -> Smart search -> Overview.
 

Page url: http://devnet.kentico.com/docs/5_5r2/contexthelp/index.html?searchindex_sites.htm