An Introduction
to PHP

PHP is an acronym for "PHP Hypertext Preprocessor".  PHP is both a scripting language which can be embedded in a text file, and an interpreter for that scripting language.  The context usually implies which of the two is being referred to.

PHP is usually used with a web server to provide dynamic content for a website.  PHP scripts can be used to process web form submissions, to take web page content from a database, to store information in a database, to perform calculations, to modify page content depending on the browser being used, to implement a shopping cart, to provide a discussion board, to send E-Mails, to upload files, ...

PHP is a server-side scripting language.  This means that PHP processing is done by the web server before the page is sent to the client browser.  The browser never sees the PHP code itself, but sees only the result of the execution of the code.  (Javascript, on the other hand, is usually a client-side scripting language.  This means that the Javascript code is sent to the client browser as part of the web page, and is then executed on the client system by the browser.)