FOSS stands for free and open source software. It refers to software that provides users with four essential freedoms: the freedom to use the software for any purpose, study and modify the source code, redistribute copies, and improve the software for the whole community. Some key benefits of FOSS include no licensing fees, ability to modify without permission, and many choices of software. Popular FOSS alternatives to proprietary software include Firefox, OpenOffice, GIMP, Blender, QCAD, Scribus, Moodle, MPlayer, MythTV, and R Project for statistical analysis.