A subweb is a subdirectory of a web site created with FrontPage that behaves just like a complete web site — essentially a web site within a web site. Like your top-level web site (your root web or root directory), subwebs can contain any number of subdirectories, and even contain additional subwebs. You can assign each subweb a different set of authors and permissions, independent of your root web. With subwebs you can grant others the ability to access, edit, and publish to your site while protecting your root directory and your root web user name and password.
For example, you might create a subweb at your domain for posting information relevant only to your employees. When you set permissions for this subweb, you could limit access to employees only (keeping it from the eyes of the public) and give managers a user name and password with which they can edit and republish the pages.