Open-source refers to a philosophy of software development that emphasizes collaboration, transparency, and sharing of source code. The idea behind open-source is that by making code freely available to the public, developers can build on each other's work, collaborate on projects, and innovate more rapidly. Open-source software can be used, modified, and distributed without restrictions, which has led to the creation of many popular and widely-used software products, such as the Linux operating system, the Apache web server, and the MySQL database. The open-source movement has had a significant impact on the technology industry, enabling the creation of new software solutions, promoting innovation, and fostering a culture of collaboration and knowledge-sharing.