What exactly is tumblr.?

Basically its a website where あなた have your own website. あなた post pictures, videos, anything and people follow you,=. It's basically a blog. If あなた follow someone, their posts 表示する up on your dashboard. It's really awesome.
Here are some exmples.

laynemorgan.tumblr.com
unexpectedrandomness.tumblr.com
dirtytuscon.tumblr.com
asdfghjkllove.tumblr.com
katuriankaturiankaturian.tumblr.com

and the entire Pophangover.com is basically a big TUmblr website.