PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.
PHP can generate dynamic page content
PHP can create, open, read, write, and close files on the server
PHP can collect form data
PHP can send and receive cookies
PHP can add, delete, modify data in your database
PHP can restrict users to access some pages on your website
PHP can encrypt data
With PHP you are not limited to output HTML. You can output images, PDF files, and even Flash movies. You can also output any text, such as XHTML and XML.