Hello
I'm developing an Android application and it will not be free. I'd like to change font in it.
Can i use font 100% free for commercial use?
Which is the difference between 100% free and Public domain / GLP / OFL ?
What does they mean exactly ?

Google it. First understand the definitions and then ask. If there is any need at all. Which there is not.

If you know the email address of the author of the font, send him an email and ask him if you can use the font for commercial purposes.

If private messaging here at Dafont is enabled for the font author, send him a private message and ask.

See if there is a text file inside the ZIP file that you downloaded here at Dafont where the font author might have stated his conditions for the use of the font.

See the font's copyright field if the font author left any instructions there. The copyright, however, is not shown in the Font Viewer of Win7 .