This is why we say “free and open source”, free software (not to confused with “freeware”), or FOSS (Free and Open Source Software), with sometimes added explanation of “free as in freedom” in many more formal setting. Meaning that these software comes with several essential right and align with the ideology of the free and open source movement.

In most daily conversation, open-source is really short for the “free and open source software” described above.

Also “source” code, i.e. “where the software cames from” is different from machine code, which makes up the actual executable you run on your computer. Source code includes comments and sometime inefficiencies to make it human readable, the compiler strips these component and translate it into a language where only machine can understand. This is for legitimate performance and compatiblity reason.

Although there are process of decompilation, where people try their best to revert the translation, the “source” code is still not avaliable to you, since many things will simply gets removed by the compiler, and hence non-recoverable from just the machine code.