Open source is anything that you come across on the Internet that has been made available for public use for free. It can be used, modified, and built without any problems.
The term "open source" was originally used in reference to open source software (OSS). Code for open-source software is code that is created to be publicly accessible so that anyone can see it, alter it, and share it as they see fit.
Peer review and community production contribute to the development of open-source software, which is developed in a collaborative and non-centralized manner. Since open-source software is developed by communities, as opposed to a single company or author, it is often more flexible, cheaper, and more durable than its proprietary counterparts.