LAMP is actually a combination of 4 different technologies, namely, Linux, Apache, MySQL and Perl/PHP. This technology is the most popular server system today. The term LAMP originated as a marketing term to prove that a combination of free softwares can be as effective as costly ones such as J2EE and .NET.

Linux
It serves as an alternative to Microsoft Windows. Millions of people use Linux and create programs for the same. It has been derived from Unix and hence is very fast and stable. Linux works very well on web servers.

Linux has a number of varieties, called 'distributions'. Each version focuses on different features. Some of the popular distributions include Debian, SuSE and Red Hat.

Apache
It is the most popular web server on web. It was developed at NCSA by Apache Foundation in 1995. It has since then become an industry standard. It is included in software packages such as Oracle and WebSphere.

MySQL
MySQL is a database and is available for free. It is easy to set up and manage. However, it is quite controversial among professional as it does not include a number of advanced features that would have made it easy to use. It has been developed by MySQL AB, which is a Swedish company.

Perl and PHP
PHP and Perl are both scripting languages. They make the database driven websites to work. Both these languages are very different from each other. Perl is hard to read but powerful, whereas PHP is simpler but limited. Sometimes, Python is also used as an alternative language.

PHP is better suited for beginners whereas Perl is meant for people with previous programming experience.

Getting LAMP
You can get the entire system together at www.apachefriends.org/en. There is no need to download the individual component separately. The entire software is available for free. Linux is not given, but the others can be easily installed on all operating systems such as Windows and Linux.

LAMP Variants
There are few variants of LAMP that can replace a part of the system. Though they are not popular but you should have knowledge about it.

WAMP: Windows replaces Linux.
AMP: Apache, MySQL and Perl/PHP running on any operating system.
MAMP: Macintosh Operating System replaces Linux.

Another term exists called WIMP, which stands for Windows replacing Linux and IIS replacing Apache. However, the term sounds very offensive and  results in a much worse system than LAMP.