High-definition video generally refers to any video system of higher resolution than standard-definition (SD), i.e. NTSC, PAL and SECAM. It is important to note the difference between general purpose high-definition video as discussed in this article, and its specific applications in television (HDTV), professional acquisition (HDCAM, HDCAM-SR, DVCPRO-HD & D5-HD), consumer acquisition (HDV) and optical disc systems (Blu-ray and HD-DVD).
Reference link: *en.wikipedia.org/wiki/High-definition_video
So, tomorrow, if you buy bluray/HD-DVD, you can connect a HD monitor and watch HD movies in High definition.
Video Tape -> CD -> DVD -> HD-DVD/bluray
The above tree should clear your doubt.
Note: high def drives/monitors/movies have very high pricing. But will come down soon. If there isn't much difference in price between gigabyte and asus motherboard, go for Gigabyte. Who knows, you might buy a HD-DVD or bluray drive and HDTV tomorrow.