Once a tenant and site are created and/or a theme is manually created you may want to assign a theme to a site. A theme is automatically assigned when during a site creation but what if you want to assign a theme to already created site.
Sitecore supports multitenancy, which means you can have multiple sites running on a single Sitecore instance.
Tenant folder is just a container to hold multiple tenants you may have as a part of site structure. Inherited from _Base Tenant Folder. You may create a tenant folder to hold the multiple tenants of a Company.
A folder with provide tenant folder name is create here – /sitecore/templates/Project/<Tenant Folder Name>