WebDAV was initially created as a protocol for managing web server content over http/https. In other words, it grants you the ability to add, remove, or edit HTML and support web content remotely.
From there, the usage expanded to provide access to general file services as well. For example, Apple's iDisk service (part of iTools/.Mac/MobileMe) supported accessing your files through any WebDAV client. This support unfortunately ended when iDisk was retired with the transition to iCloud.
WebDAV clients are built into Mac OS X and Windows as well as the file managers for Gnome, KDE and many other Linux desktop environments. You can even find Linux console tools, which support the protocol or mount it directly on your filesystem using the davfs2 filesystem driver.
