PHP is an imperative scripting language, primarily used for creating web-based apps. PHP's popularity has soared in recent years, due to a relatively small learning curve, and an extensive set of built-in library routines.
The syntax of PHP has evolved over the years. PHP2 looked like BASIC. PHP3 resembled a hybrid of C and Perl. PHP4 maintained the C and Perl-like aspects, while adopting some Java-like constructs. PHP5 promises to look even more like Java.
The origin of the name PHP is ambiguous, at best. Candidates include Personal Home Page, Hypertext Pre-Processor, PHP: Hypertext Processor, and the like. Regardless, the name stuck. The PHP manual itself states the name of the original languge (PHP/FI) as Personal Home Page Tools, and its current successor (that which we know as PHP) as PHP: Hypertext Pre-Processor. The relevant page of the manual is http://www.php.net/manual/en/history.php.
PHP is rich and a number of database libraries are availible, this include MySQL and mSQL. The popularity of PHP is growing and many hosting companies, free and paid are now offering it as part of the hosting. PHP is dangerous in the sense that many crackers exploit its popularity and find holes in the system, there have been real situations where people have been cracked because of PHP ( recently the Descent 2 Open Source (d2x) site was cracked using a hole in PHP ).
There is also PHP-GTK, qouting its website: "PHP-GTK is an extension for PHP programming language that implements language bindings for GTK+ toolkit. It provides an object-oriented interface to GTK+ classes and functions and greatly simplifies writing client side cross-platform GUI applications."
Links: