A Public Folder is a shared hosted Exchange folder that is automatically visible to all Users within the Exchange account that have been granted permissions to the folder.  This folder will automatically show up in those Users' Outlook (with AutoDiscover) and OWA clients.  Public Folders provide a company an easy method to share Email, Contact, or Calendar data with multiple users.

On creation, each Public Folder must have at least one Owner User.  The Owner is able to grant permissions to the Public Folders to other Users, and create subfolders under the Public Folder.  No other Users will be able to access the Public Folder until an Owner has granted them permissions.

A Public Folder added via the Control Panel is a Root Public Folder.  This folder is always an Email content type folder.  Subfolders, including Calendars and Contact Lists, can be created under the Root Public Folder.  For a User to be able to access a Public subfolder permission must be granted to the subfolder and any parent folders, up to and including the Root Public Folder.