What is open source software

Open source software(OSS) is a software that's distributed with its source code which can be modified i.e it can be read/updated by the programmers/users according to their need.
It includes a license for programmers to change the software for their purpose.
OSS is usually developed as a public collaboration and made freely available.
OSS should meet with following criteria,
• The software must be redistributed
• The source code must be made available
• Programmers'/users should be able to modify the code
• It should be freely distributed
• The license can require improved versions of the software to carry a different name or version from the original software.