Work Folders is a new feature of Windows Server 2012 R2 that is designed to allow personally owned Windows 8.1 and Windows RT 8.1 tablets and laptops to sync business-related files and folders with a share on the corporate network.
Additionally, administrators can wipe the synced data because it is stored in a segregated way, and it's signed by a separate encryption key, so that the user's personally owned content, like photos and files, can be left intact after a wipe.
The key bit in all of this is the sync share. The sync share is essentially how Windows Server 2012 R2 manages which files to sync for which users. You set up a sync share by establishing a folder locally accessible to a Windows Server 2012 R2 server, and then pointing a wizard to that location. Within that shared folder, each user will have a subfolder that will contain the files that the Work Folders feature will host and sync.