Closed Source Vs. Open Source

Today in class we learned the differences between open sources, and closed sources. Closed source software (i.e. Microsoft Windows and Office) is made by a single person or a company. The final program that you run on your computer is all that is available. The actual source code for making the software is kept a hidden and unchangeable. Open source software on the other hand, is basically the complete opposite, it's usually free to use and the source code is open to the users to alter to their liking and even re-sell it!