WordPress Installation Templates are the templates that you design which you can use to kit-out your WordPress sites.
You can create your own templates within the iControlWP User Interface which lets you to search WordPress.org and then just click to add that to your installation template. (See an example below)
iControlWP will store that plugin/theme into your template. Then, when you deploy a template, iControlWP will take each plugin and theme listed within it and install it on the given site. (See an example below)
For more information on WordPress Installation Templates, read the blog article here.