…a variation of a blog, that favors short-form, mixed-media posts over the longer editorial posts frequently associated with blogging. Common post formats found on tumblelogs include links, photos, quotes, dialogues, and video. Unlike blogs, this format is frequently used to share the author’s creations, discoveries, or experiences without providing a commentary.
Some people have an impression that cool people blog using WordPress. Well I’ll be twice as cool then for managing two. 
Their mindset probably came from the fact that Wordpress, though free to download, originally requires having your own web host and back in those days, web spaces cost gold! Then when they came up with the hosted version two years ago, it was with an invite-only system. Some people even made money out of it by selling those invites on eBay for as high as $90!
WordPress is a state-of-the-art semantic personal publishing platform with a focus on aesthetics, web standards, and usability. What a mouthful.
WordPress is both free and priceless at the same time. More simply, WordPress is what you use when you want to work with your blogging software, not fight it.