That's right. Open Source typically means OSI approved license. Sadly, Open Source gets used as a term to refer to things that are inclusive in some way, or where access to source code is given without the bundle of rights associated with OSI approved licenses.

As RMS says, all Free Software is open source. I believe the converse statement to be true always or nearly always all the time. Though the licenses are the same, the guiding philosophies are different. Open Source tends to focus on the benefits of openness, such as quality resulting from many reviewers. By contrast, RMS and the Free software folks will tell you that quality isn't the primary aim--the 4 freedoms are.

In terms of licenses, Copyleft licenses are a subset of Free and Open Source licenses that restrict the ability to make derived works non-Free/Open. E.g. BSD is Free software, but not Copyleft.

To give a concrete counterexample:

one of my favorite video games, Descent, has been open source for about 15 years. I have four different source ports on my system right now (d1x, rebirth, retro, and d2x-xl) each of which is free to download, install, run, and even modify. But some of the game assets (textures, ship polymodels) are not free; you must buy a copy of the game [0] to acquire a license to those asset files, or play using only the shareware assets [1].

[0] http://www.gog.com/game/descent_1_descent_2 or http://steamcommunity.com/app/273570

[1] prepackaged with the rebirth/retro ports at http://descendentstudios.com/community/topic/1167-descent-sh... , where they're being used as a marketing tool for the currently-being-kickstarted Descent:Underground game at https://www.kickstarter.com/projects/descendentstudios/desce...