What is PHP?

PHP is a scripting language, somewhat similar to Perl, but designed from the outset for web development. It can also be used on the command line and for developing GUI applications (PHP-GTK), but in this book we will concentrate on the use of PHP as a web server module. Unlike the client side JavaScript (ECMAScript) and Java applets you see in your web browser, PHP scripts generally run on the server.

Because PHP is a scripting language, there is no need to compile your code before running it, as you would need to do for, say, a C program. This means that it runs slower, but development is faster. PHP code can actually be embedded into HTML pages, allowing you dynamically generate page elements. It is both a simple and very powerful language.