The acronym LAMP refers to first letters of the components of the solution stack composed entirely of free and open-source software to build high-availability heavy duty dynamic web sites that can serve ten thousands of requests:
Linux, the operating system;
Apache HTTP Server, the Web server;
MariaDB or MySQL, the database management system;
P for PHP, Perl, or Python, the scripting languages (respectively programming languages) used for dynamic web pages and web development.
The exact combination of the software included in a LAMP stack is prone to variation, e.g. Apache web server can be replaced by some other web server software. Though the original authors of these programs did not design them all to work as a component of a LAMP stack, the development philosophy and tool sets are shared and were developed in close conjunction, so they work and scale very well together. The software combination has become popular because it is entirely free and open-source software, that means that each and every component can be adapted to the underlying hardware solution and customized to meet job specification as exactly as possible without the slightest vendor lock-in. The complete software stack also happens to be free of cost, leaving maximum financial leverage to be put into the tailoring of the entire hard- and software solution, which can be outsourced to external contractors.
Due to the nature of free and open-source software and the ubiquity of its components, each and every component of the LAMP stack is very well tested regarding performance and security and there is an abundance of experienced contractors to do the tailoring respectively the system administration. There is also a constant development going on.
The components of the LAMP stack are present in the software repositories of most (if not all) Linux distributions, giving any end-user a simple way to install, set up and operate an initial LAMP stack out of the box. The web presence of a small company which does not have a high hit count and is not prone to frequent attacks, can therefore be administered by another small company, by a one man company or even by a student.