A vlog or video blog is a blog (short for weblog) which uses video as the primary content; the video is linked to within a videoblog post and usually accompanied by supporting text, image, and additional meta data to provide context.
Diavlog, by the same token, is a video dialog. It follows a blog format in that it accompanies video clips with meta data relevant to the video. A diavlog could come out of a web cam recording, a video conferencing session, or even, a video by email sequence that grows with each response.
Blogs often take advantage of RSS or Atom for syndication to other web sites and aggregator software (feed readers). With development of RSS enclosures, which provide the ability to attach media files to a feed item/blog post, or the use of the Atom format (which supports rich media content by design) it is possible to bypass the mainstream intermediaries and openly distribute media to the masses via the Internet. Vlogs typically take advantage of this technological development, just as audioblogs have in recent years via the podcast boom.
As of 2006, videoblogging is rising in popularity, especially since the release of the new Apple Video iPod and the availability of iTunes Store's video content. iTunes uses the term video podcast to describe a video blog.
One of the potential problems with Vlogs is the current inability of search engines to create rich metadata or "search engine" data from the stream. For Vlogs to be fully embraced as part of web culture, some indexing solution will need to emerge.
(Some definitions taken from Wikipedia, the free encyclopedia, New: Vidize.com focuses on video sharing and personal broadcasting)