WebDAV is an abbreviation for Web-based Distributed Authoring and Versioning. Its commonly just called DAV. WebDAV is an open standard that technically enhances the HTTP/1.1 protocol providing mechanism like write support.
There are many ways to use WebDAV on NetBSD.
Gnome supports by default webdav mounts.
You can use Konqueror to mount a remote DAV Server.
Another possibility is to install the package www/cadaver. This is a command line tool to access DAV servers.
With fuse-wdfs you can mount webdav directories and access subversion repositories like a usual mountpoint. [Fuse] requires puffs to be built in your kernel.