PHP (recursive acronym for PHP: Hypertext Preprocessor) is a widely-used Open Source general-purpose scripting language that is especially suited for web development and can be embedded into HTML.
In an HTML document, PHP script is enclosed within special PHP tags. Because it is embedded within tags, the author can jump between HTML and PHP rather than relying on heavy amounts of code to output HTML. Additionally PHP is executed on the server therefore the client cannot view the PHP code.
PHP can perform any task similar to CGI program. However its strength lies in its compatibility with many types of databases. Also, PHP can communicate across networks using IMAP, SNMP, NNTP, POP3, or HTTP.