Briefly, FOSS programs are programs whose license gives users the freedom to run the program for any purpose, to study and modify the program (without having to pay royalties to previous developers).

Linux is a computer operating system just like Microsoft Windows. The Linux operating system is free and open source software. Linux as a platform embodies the rest of the programs that are considered FOSS.

It’s important to ensure the terms free and open are used in the proper context. Software is considered open if the developer avails the source code with the distribution of the finished product. This means that the user can actually modify the program if need be to suit his or her operating environment or application. Freedom is freedom as in speech. This means that the user is free to use the software as outlined above.

On the other side of the coin, we have the closed proprietary programs distributed by software vendors like Microsoft, e.g. Microsoft Windows operating system and Microsoft Office suite. In this case, the software vendor or developer does not avail the source code. The user therefore cannot do any modification on the software, and has to rely on the software vendor for patches and upgrades.