"Briefly: WebDAV stands for "Web-based Distributed Authoring and Versioning". It is a set of extensions to the HTTP protocol which allows users to collaboratively edit and manage files on remote web servers."
http://www.webdav.org/
WebDAV (Web-based Distributed Authoring and Versioning, also called DAV) is a set of extensions to HTTP/1.1 (HyperText Transfer Protocol, the protocol spoken by Web browsers and servers) allowing you to edit documents on a remote Web server.