Proprietary software also known as "Closed Source Software" is non-free computer software for which the software's publisher or another person retains intellectual property rights—usually copyright of the source code, but sometimes patent rights.

- extracted from Proprietary Softwares, Wikipedia as on 30th December, 2018

Open-source software (OSS) is a type of computer software in which source code is released under a license in which the copyright holder grants users the rights to study, change, and distribute the software to anyone and for any purpose. Open-source software may be developed in a collaborative public manner. According to scientists who have studied it, open-source software is a prominent example of open collaboration.

- extracted from Open-source software, Wikipedia as on 30th December, 2018

In simple terms, software is written in one language. This constitutes the source code. This code is compiled to machine code, which is then distributed. If source code is "4+5", then compiled form is analogous to "9". Knowing "9", you cannot tell whether it was "6+3" or "4+5" or anything else. Here, is a more technical explanation.