DVD stands for "Digital Video Disc" and refers to a very common optical storage disc. DVDs are used primarily for movies, though they can also be used for computer data storage. DVDs replaced VCR tapes as the preferred format for home video viewing in the mid to late 1990s.
Blogs that utilize the DVD tag fall generally into two groups: sites that deal with movies (reviews, news, etc.) and sites that deal with technology. In some cases, these groups overlap in blogs that cover both movies and the technology used to watch them.
Some DVD blogs in the "movies" group include horrorsnotdead.com and filmjunk.com for example, while itechnews.net and cybertheater.com are examples of the "technology" group of DVD blogs. dvdtalk.com is a wonderful example of a blog that features both movie reviews and info as well as tech updates and buyer's guides.