WOFF - Web Font Files
Web Font Files with the extensions .woff and .woff2 can be found in browser caches.
They are compressed versions of TrueType of OpenType Fonts. You make woff files from regular TTF or OTF files with font compression tools so you can make sure the special font you are using is available on the browser reading the page.
You can also find free fonts with google, and you can use Googles selection of web fonts