Open source vs. proprietary software
Proprietary software is administered, maintained and published by corporations and businesses whose main interests are profits and maintaining control over the code and use of their product. It can be restrictive and expensive.
Only the original authors of proprietary software can legally copy, inspect, and alter that software. In order to use proprietary software, users have to agree that they will not do anything with the software that the software's authors have not expressly permitted. (Think about the EULAs you have to agree to in order to use Adobe, Microsoft or Apple products.)
Open source software offers no such restrictions. The authors make the source code available for anyone who would like to view, copy or alter it. Open source incorporates a belief that code is only made better by sharing and learning. Further, anyone who alters and shares a program with others must also share that program's source code without charging a licensing fee for it, keeping it free to use and modify.
Open source software is inclusive: there is a community of users and developers in the people who produce, test, use, promote, and ultimately affect the software they love.