As part of the Channels module, a site is where the information from the module Content is displayed in order to create your own custom digital channel. The operations for development, design, and navigation flow are also included.
In a Site, you have complete control of what you display using Pages, the menu from a Site is created using Navigation, you can create custom Widgets, and the look and feel is customized using Templates.
You can find more information about Sites in our documentation.