Comment 4 for bug 630731

The term "Gratis" unambiguously identifies zero-cost software, doesn't it?
I'd also prefer if the term "Free Software" were used to identify Free Software as referred in Ubuntu's mission statement:

"The vision for Ubuntu is part social and part economic: free software, available free of charge to everybody on the same terms, and funded through a portfolio of services provided by Canonical."
http://www.ubuntu.com/project/about-ubuntu

If you must refer to Open Source, I'd suggest considering using the term "OSI Certified License" and refer to:
http://www.opensource.org/licenses/index.html