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_ssl is an optional module for the Apache HTTP Server. It provides strong cryptography for the Apache web server via the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) cryptographic protocols by the help of the open-source SSL/TLS toolkit OpenSSL.
OpenSSL is a software library for applications that secure communications over computer networks against eavesdropping or need to identify the party at the other end.
PHP is a general-purpose scripting language used for web development.