Open Source Software allows developers to freely access, modify, and share the source code for a piece of software. It is created by an author or company and then made available for free distribution. Open source software projects can involve thousands of programmers collaborating to refine a product. There are many advantages like no upfront costs, rapidly evolving code, and the ability to customize software. However, there are also disadvantages like potential lack of support if a project becomes abandoned and not all community suggested features may be implemented. Popular examples of open source software include Linux, OpenOffice, Firefox, HTML, and Apache.