Open Source is the same thing as Free Software, just with the different name. The term "Open Source" was coined later to emphasize the business benefits instead of the rights and freedom of the users, but the four freedoms of the Free Software Definition [1] and the ten criteria of the Open Source Definition [2] describe essentially the same thing.

[1] https://www.gnu.org/philosophy/free-sw.en.html

[2] https://opensource.org/osd