Apache is a web server software. Its full name is Apache HTTP Sever, and it is currently the most used web server software in the world. It is free and compatible with operating systems like Microsoft Windows, OpenVMS, NetWare, but it is mostly used with Linux.
Apache is open-source, as well as free, which means that it is openly distributed among people, and anyone has the ability to develop and improve it.
Apache has many various features. Some of them are:
and many more.
Apache is part of the LAMP stack.