Some multimedia players, such as vlc, can act as a client or a server, in addition to just being a conventional media player.
As a server, vlc allows clients to connect to it, and streams out A/V stream to the clients. One can run vlc in server mode on a machine with a DVD player to play a DVD. Then, a netbook computer without a DVD drive can run vlc to connect to the computer with a DVD player. This way, the user of the netbook can also play the content of a DVD loaded on the other computer with a DVD player.
Note that this is not the same as file sharing, as the content of the DVD is not shared. To play a DVD remotely using file sharing, a lot of network bandwidth is needed (as DVDs use MPEG2 encoding, which does not compress video very efficiently).
vlc supports on-the-fly transcoding. This means that a DVD source (using MPEG2) can be transcoded into MPEG4 (much more compressed without loss of a lot of quality) before the stream leaves the server. This makes it possible to watch a DVD remotely even using a modest IEEE 802.11g network (supporting up to 54Mbps, in theory).