What does it mean that Plone is open source?

Plone is open source software. This means that you enjoy four fundamental freedoms with Plone:

The underlying source code of Plone is freely-available for anyone to look at, modify, and distribute. Plone is licensed under the GNU Public License (GPL), which guarantees this freedom, and requires that anyone who distributes modified versions of Plone do so under an equivalently free license.

The Plone codebase is owned by the Plone Foundation, a US-based 501(c)(3) nonprofit corporation. The Plone Foundation, which was created with help from the Software Freedom Law Center, is modeled on the highly successful 'software conservancy' model of the Apache and Mozilla Foundations. The Plone Foundation provides legal protection for Plone, enforces its licensing terms, and promotes Plone and the Plone community. The Plone Foundation does not direct the development of Plone—the Plone community does that.

People who make substantial contributions to the Plone community can apply for membership in the Plone Foundation. The Plone Foundation is governed by a board of directors that is elected by the membership of the Foundation.

For more information about Plone's licensing terms, see http://plone.org/about/copyright. For more information about the Plone Foundation, see http://plone.org/foundation.