Open source does imply rights to alter and redistribute:

https://opensource.org/licenses https://opensource.org/faq#free-software

The terms Free Software and Open Source are the same from a technical point of view, to the extent that they describe the same set of software. However, they are different in that they connote different views about the world---people saying free (or libre) software take a stance in that software should be free in order to build more just society, while people saying open source don't necessarily take a political stance with regard to software, and often see licensing only from a business point of view.