PHP is a server-side scripting language used to build dynamic web applications. It allows developers to add interactivity to websites. Some key points: - PHP scripts are executed on the server-side and allow generation of dynamic web page content. - It supports many databases and is compatible with popular web servers like Apache and IIS. - Basic PHP syntax involves opening and closing <?php ?> tags to embed PHP code in HTML documents. - Variables, conditional statements, loops and functions allow building complex scripts. - PHP can retrieve and process form data submitted from HTML forms.