Board Thread:Plants vs. Zombies 2/@comment-25546049-20150703183553/@comment-5079138-20150815234237

Well, "open-source" means that the program is free, AND you can look at the source code, and possibly the beta builds too (which are unstable). If you're a programmer, basically you can just look at the source and then implement it to the program without needing 1Zulu to do the job first.

And the source code can be altered in any way you want, but you need to include and retain the GNU GPL license or any other licenses available.