What does “Open Source” means?

OK, so we’re using MS .NET technologies for years. We are also work in a company that declares itself as a “community of professional software developers”. But it is “Open Source”? What is “Open Source” software and what is it good for? Who gains from Open Source SW usage, and Why?


Answers to all of these questions and more, can be found in a very good presentation about Open Source usage made by Segev Levi, a former manager at XLNet.