Plex is a media server platform that allows users to organize, stream, and share their personal media collections, such as movies, TV shows, music, and photos. It can be installed on various devices, including computers, NAS (Network Attached Storage) systems, and some smart TVs. Users can access their media library from anywhere with an internet connection, making it convenient for on-the-go viewing. In addition to personal media, Plex offers a range of free ad-supported content, including movies and TV shows. The platform also supports various features like live TV and DVR capabilities, enhancing the overall media experience for users.