Closed Source is software that is generally not free, where the source code is safe and encrypted. Contrary to Open Source, Closed Source can’t copy, modify, or delete parts of the code without consequence. Consequences can go from voiding a warranty to legal repercussions. Open Source software has a “mass collaboration” approach, where Closed Source software developers are the ones that generally handle the development and fixes, meaning it is under their discretion if they continue their ongoing development or not. Closed Source software is something that cannot be widely distributed due to licensing that comes with the products. Examples of Closed Source software would be Windows, Microsoft Office, Skype, or Internet Explorer.
Source: Veriday
Additional Reading: MIT Tech Review Downgrades Aarogya Setu Rating, Source Code for App Made Public
Related Terms: COTS Software, Open Source, Software Development Life Cycle (SDLC)