> Q. Is Lumberyard “open source”?
> No. We make the source code available to enable you to fully customize your game, but your rights are limited by the Lumberyard Service Terms. For example, you may not publicly release the Lumberyard engine source code, or use it to release your own game engine.
So according to them it's not even "open source".
If it is open source software (which this is emphatically and expressly not), it is FOSS.
You can charge as much as you like for FOSS[2].
Open Source is not the same as Source Available[3].
1. https://en.wikipedia.org/wiki/Free_and_open-source_software
2. https://www.gnu.org/philosophy/selling.en.html
3. https://en.wikipedia.org/wiki/Open-source_software#Open-sour...
