The term “open source” refers to something that can be modified because its design is publicly accessible. Open-source software is software whose source code is available for modification or enhancement by anyone but need not be free of charge.
Its developers make its source code available to others who would like to view that code, copy it, learn from it, alter it, or share it. LibreOffice and the GNU Image Manipulation Program are examples of open-source software.
Open-source software licenses allow other people to make changes to source code and include those changes into their own projects. Some open-source licenses make sure that anyone who alters and then shares a program with others must also share that program’s source code without charging a licensing fee for it.