What is open-source software?

Open-source software is the kind of software whose code is available to see.
The code is not hidden and can be freely inspected - and even modified.

On the other hand, proprietary or closed-source software is the one
whose code remains hidden. The ‘proprietary’ adjective stems from the fact that
it remains the property of its creator, which is rarely the case with open-source software.

open-source communities are extremely interested in reviewing and proposing
changes to the code to make it more secure.
Therefore, open-source projects have the advantage of the community.
On the other hand, closed-source software has secure codebases, making them less likely to be exploited.