Apache is a free and open-source cross-platform web server software.
Debian is a Linux software which is a free open-source software.
Mod_perl is an optional module for the Apache HTTP server. It embeds a Perl interpreter into the Apache server. In addition to allowing Apache modules to be written in the Perl programming language, it allows the Apache web server to be dynamically configured by Perl programs.
Unix is a family of multitasking, multiuser computer operating systems.