LAMP is an archetypal model of web service solution stacks, named as an acronym of the names of its original four open-source components:

the Linux operating system, the Apache HTTP Server, the MySQL relational database management system (RDBMS), and the PHP programming language. The LAMP components are largely interchangeable and not limited to the original selection. As a solution stack, LAMP is suitable for building dynamic web sites and web applications.

Originally popularized from the phrase "Linux, Apache, MySQL, and PHP", the acronym "LAMP" now refers to a generic software stack model. The modular componentry of a LAMP stack may vary, but this particular software combination has become popular because it is entirely free and open-source software. This means that each component can be theoretically interchanged and adapted without overt vendor lock-in, and that the complete software stack is optionally available free of cost. The components of the LAMP stack are present in the software repositories of most Linux distributions, provisioning a LAMP stack with some automation.