Georgia  Suggested by pantextual 

Georgia. If you're on Windows or Mac, you should have this pre-installed.

thank you very much! Do you know if exist a lighter version?

There's an expanded version called Georgia Pro; however, it'll set you back a bit of money if you want the light version. The version of Georgia that comes with OS X and Windows just has Regular, Bold, Italic, and Bold Italic.

http://www.myfonts.com/fonts/ascender/georgia-pro/

link to that web, please

Isn't that just a regular tweet ?

Don't know, mate, I don't use Tweeter

Me neither actually