Can open source be used for commercial purposes?

Related questions

1. Is my SQL free?
2. Can Lgpl be used in commercial software?
3. What is the difference between gplv2 and gplv3?
4. Can I use MySQL for free?
5. What is GPL and GNU?
6. What is the purpose of GNU General Public License version 3?
7. Is MySQL owned by Oracle?
8. What does the G in GNU stand for?
9. Is LGPL open source?
10. What is AGPL software?

Tags

1. #purpose
2. #commercial
3. #however
4. #source
5. #proprietary
6. #definition
7. #software
8. #guarantees