Tumblelogs are to weblogs (aka ‘blogs’) as Twittr is to social networks like Facebook. Bloggers decided to strip down their lengthy diatribes in favor of postmodern collages and/or collections of lean quotes, text, blurbs, photos, YouTube links, etc.
Exercises in brevity or the end of civilization as we know it (again)? Even if you decide the latter, it seems that the upside of the trend is an increasing development in web applications that allow users to quickly set up spaces to create rich media (ie: videos, sound, images, text) sites (most notably some lightweight content management systems, such as Gelato)
More info on tumblelogs:
Kottke.org has a nice write up with some sensible thoughts about the tumblelog phenomenon.
Of course, Wikipedia has an entry on it as well…although I haven’t seen anyone else using the term ‘tlog’…but that’s Wikipedia for you.
Here’s some examples for the curious:
https://www.tumblr.com/ (also provides a tool for creating tumbelogs)