Websites can be a lot like a swan swimming on a lake; above the surface, the swan glides serenely, but underwater the webbed feet are furiously churning away to provide forward motion.
All we usually see is the glossy surface of the web, and have no regard for all the whirring and clicking going on "in the back".
A lot of times, that whirring and clicking is provided courtesy of LAMP, a set of freely available, open source software products - also referred to as a "LAMP stack". While these are independent products, they tend to be used together and so the LAMP acronym stuck.
The four software components are Linux, Apache, MySQLand PHP (sometimes Perl or Python replaces PHP).
Linux - the operating system running the web server computer
Apache - the web server software that allows pages to be displayed
MySQL - the relational database server that manages web site data
PHP, Perl, Python - the scripting language used to build dynamic web pages
Not something you need to know as a web user, but it's good water cooler fodder!