a computer program may be open source, which means the source code is shared with anyone who wants to look at it and change it. many programs are however closed source, which means only the executable code is distributed and people are not allowed to look at and change the code. many open source programs are also compiled to such code, that may or may not be allowed to be inspected, while to change it is most convenient to change the source code that came with it, or possibly can be downloaded.