Today morning markdown was for me the same thing as a markup.
Just a silly word. However it turns out to be a markup language which is very useful in blogging. I tried to learn some of it from wikipedia and the article which I found was pretty informative.
Try wikipedia article or this.
Why should I use it?
It's simple and easy to write. Writing < and all those html tags can be pretty tedious and you always can miss some, and usually output looks like a mess. At least for me. But there are solutions for this problem - markup languages!