XAMPP is a free and open source cross-platform web server package that is used to install Apache, MySQL, PHP, and Perl on Windows, Linux, and Mac OS systems. It contains Apache, MySQL, PHP, and Perl in an easy-to-install package that allows users to create a local web server for testing and development purposes. To install XAMPP on Linux, users download the software package, extract the files, and start the Apache and MySQL servers. The default directories for files in the XAMPP installation include the htdocs folder within the lampp folder in the opt directory.