The term "open-source" software refers to software whose original source code is made freely available for anyone to use, modify, and distribute. This model encourages collaboration and community-driven innovation, allowing developers to build upon existing software without the restrictions of proprietary licenses. Open-source software can lead to faster development cycles and improve security, as a larger pool of developers can review and audit the code. Popular examples include Linux, Apache, and Mozilla Firefox, all of which benefit from collective contributions that enhance functionality and reliability.