PHP is a language that runs millions of dynamic websites on the Internet today. It has a broad feature set, simple syntax, and support for different web servers making it ideal for rapid web application development.
PHP is an interpreted server-side scripting language. PHP script files (text files) are uploaded to a web server, like Apache, where they are interpreted producing dynamic web content.
PHP began as a set of CGI (Common Gateway Interface) scripts written by Rasmus Lerdorf. He used them to track visits to his online resume. Lerdorf called his CGI scripts the "Personal Home Page Tools" hence that name PHP today.
PHP went through numerous revisions between 1994 and 1998 with the help of software developers Andi Gutmans and Zeev Suraski. Together, the three transformed PHP into a full-fledged programming language with support for object-oriented programming. It was released in 1998 as PHP3 and provided better extensibility to various databases, protocols and APIs.
An official PHP specification draft was announced in 2014. An official PHP language specification is becoming more important as competing PHP engines are developed. The Zend Engine (a PHP interpreter), created by Rasmus Lerdorf, Andi Gutmans and Zeev Suraski, was released in 2014 and called PHP4. Facebook released a competing PHP engine called HipHop Virtual Machine. A specification guarantees that both engines maintain baseline compatibililty.