PHP stands for Hypertext Preprocessor. In fact, the product was originally called “Personal Home Page Tools”; but as it expanded in scope, a new and more appropriate name was chosen by community vote.

You can use any extension you like to designate a PHP file, but the recommended ones are php , phtml. PHP is currently in version 4, called PHP4 or simply PHP.

PHP is a scripting language embedded in HTML on the server.

The proprietary products in this market niche are Microsoft's Active Server Pages, Allaire's Coldfusion and Sun's Java Server Pages. PHP is sometimes called “the open source ASP” because its functionality is so similar to Microsoft's product/concept, or whatever.