Open-source software refers to software that is freely available to the public for use, modification, and distribution. This type of software is typically developed and maintained by a community of developers who collaborate on improving and adding features to the source code. Open-source software is often seen as a more transparent and flexible alternative to proprietary software, as it allows for greater customization and control over the software. Examples of popular open-source software include the Linux operating system, the Apache web server, and the Mozilla Firefox web browser. Open-source software has become increasingly popular in recent years, with many organizations and individuals choosing to use and contribute to open-source projects.