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.

mod_dav is an Apache module to provide DAV capabilities (RFC 2518) for the
Apache web server.  mod_dav currently implements a Class 1 and Class 2 DAV
server.  This means that it provides all the basic DAV facilities for
manipulating resources (files) on the target web server, along with
manipulating properties on those resources.  In addition, it handles the
(un)locking of resources so that clients can have exclusive access to
modify resources.