LAMP is the combination of Linux + Apache + MySQL + PHP (PHP/PERL/Python).
Linux is a free Unix-type operating system originally created by Linus Torvalds with the assistance of developers around the world. Developed under the GNU General Public License , the source code for Linux is freely available to everyone.
Apache is the most popular web server on the net. It is very secure, fast, and reliable.
MySQL is the fastest RDBMS in the world. It is very good for web based applications as well.
PHP is an open source project of the Apache Software Foundation. It is a powerful server-side scripting language for creating dynamic and interactive websites. PHP is the widely-used, free, and efficient alternative to competitors such as Microsoft’s ASP. PHP is used mainly in server-side scripting, but can be used from a command line interface or in standalone graphical applications. Textual User Interfaces can also be created using ncurses. PHP is a recursive initialism for PHP: Hypertext Preprocessor. PHP is perfectly suited for Web development and can be embedded directly into the HTML code. The PHP syntax is very similar to Perl and C. PHP is often used together with Apache (web server) on various operating systems. It also supports ISAPI and can be used with Microsoft’s IIS on Windows.