Optical disc format which is an evolution of the older CompactDisc format. Originally an Acronym for Digital Video Disc, then this was changed to Digital Versatile Disc, then finally it was deemed to stand for nothing at all, so that it could be trademarked.
DVD is an evolutionary, rather than a revolutionary, development of the same basic CD technology. By the mid 1990s, red-light lasers had become cheap enough to be incorporated into mass-market technology (as had happened with infrared lasers at the time of the introduction of the original CD). The shorter wavelength allowed the data density to be increased. This, along with improvements elsewhere in the tracking and reading systems, etc allowed the total amount of data stored to be increased by a factor of about 7, while keeping the same physical dimensions of the disc. DVDs can also have two layers, and this doubles the data storage yet again.
Another difference is that the CD were originally developed as an audio format, which was then adapted to become a computer data format. Whereas the DVD was developed from the beginning as a computer data format, which also happens to be usable for video, audio and other applications. Thus, whereas with CDs the CD-ROM data format is a special variation of the basic CD-Audio format, with DVDs it is the other way round: all DVDs are effectively "DVD-ROM" discs, and the DVD-Video format is a special case defined by a particular file structure on the disc.
Instead of the ISO9660 filesystem defined for CD-ROMs, DVDs are supposed to use a format called UDF. However, for backward compatibility, most DVDs still have an ISO9660 filesystem on them as well, albeit sharing the same file contents and layout as the UDF filesystem.
Now being used a lot more in the PC world as many computers come with DVD drives for reading or for read/write.
To play most commercial DVD movies, you need the DeCSS tool. Most distros do not include this because of legal threats from the media industry, so you need to download it separately.
There are some DVDWritingNotes found in this Wiki.