PHP is a server-side scripting language used to create dynamic web pages. It was created in 1994 by Rasmus Lerdorf and is now used by over 20 million websites. PHP code is embedded into HTML and is interpreted by the server before the page is sent to the browser. It allows developers to support databases, include files like images, and build e-commerce sites, forums, and other dynamic content without licensing fees. PHP is a flexible, scalable, and easy to use language for developing dynamic websites.