Jason Kottke defined tumblelogs as:
a quick and dirty stream of consciousness, a bit like a remaindered links style linklog but with more than just links [...] with minimal commentary, little cross-blog chatter, the barest whiff of a finished published work, almost pure editing...really just a way to quickly publish the “stuff” that you run across every day on the web. [They have] different ways of displaying various types of content...remaindered links, regular posts, book reviews, and movie reviews are all displayed differently.
Perhaps the best implementation of this model is Tumblr, a simple hosted tumblelog service that allows you to post text snippets, photos, quotes, links, chat logs, audio files, or video files. While an excellent service, it is a bit limiting; post formats are restricted to those seven things. If you would like a standard format to your recipes or code snippets, you’re out of luck.
django-tumblelog is an attempt to provide more flexibility to this format by giving you full control over each post type.