> In most cases (vast majority?), Open Source software (as defined by the OSI) is also Free (as defined by the FSF).
It is a bit tricky here. Based on the situation, the same software can be some times be open source AND free software, or open source only (ie, not free software).
Eg: Linux kernel. When it is run on your computer, usually it is mostly free-software (linux-libre would be fully free). When it is run on your router, they (vendor) shall give you the source code, but may not allow you to modify it. This is violation of freedom 1 (The freedom to study how the program works, and change it so it does your computing as you wish). Then it won't be a free software, but just open source. You can't even confirm whether the source code they gave corresponds to the binary run in the router.
It is a bit tricky here. Based on the situation, the same software can be some times be open source AND free software, or open source only (ie, not free software).
Eg: Linux kernel. When it is run on your computer, usually it is mostly free-software (linux-libre would be fully free). When it is run on your router, they (vendor) shall give you the source code, but may not allow you to modify it. This is violation of freedom 1 (The freedom to study how the program works, and change it so it does your computing as you wish). Then it won't be a free software, but just open source. You can't even confirm whether the source code they gave corresponds to the binary run in the router.