Any one.
You can for example define a slave site
Site id = slave1
domain =
www.domain1.com domain1.com
www.domain2.com domain2.com ...... {site_url}/multisites/{site_id}
deploy folder = {site_dir}
There is no limit.
You can enter several domain name in a same slave site ID.
The joomla configuration (configuration.php) file is created in the deploy directory.
The fies and directory you have given correspond to the one created by JMS when you don't deploy the slave site into its specific directory. (case of tutorial CP-03
www.jms2win.com/tutorial#jms12x-CP-03)
When you deploy a slave into a specific directory, you also have symbolic links (see video CP-04)