Software that complies with:
1. Free Redistribution
2. Source Code
3. Derived Works
4. Integrity of The Author's Source Code
5. No Discrimination Against Persons or Groups
6. No Discrimination Against Fields of Endeavor
7. Distribution of License
8. License Must Not Be Specific to a Product
9. License Must Not Restrict Other Software
10. License Must Be Technology-Neutral
see The Open Source Definition
Open source (and its definiton) is a more corporate friendly name for software libre or free software, whis namely is software that complies with the four basic freedoms:
0.The freedom to run the program, for any purpose (freedom 0).
1.The freedom to study how the program works, and adapt it to your needs (freedom 1). Access to the source code is a precondition for this.
2.The freedom to redistribute copies so you can help your neighbor (freedom 2).
3.The freedom to improve the program, and release your improvements to the public, so that the whole community benefits (freedom 3). Access to the source code is a precondition for this.
see The Free Software Definition
Software libre survey in the GX community
(you may add your own answers)