Stands for: PHP: Hypertext Preprocessor (DKF: but originally allegedly stood for Personal Home Page.)
PHP is a scripting language mainly designed for web development, where it is quite popular--arguably the single most widely-used server-side language.
This [L1 ] is PHP's home page.
For Tcl's answer to PHP, see Rivet.
In the last few years, "PHP [has become] Handy off the Web, Too", although this article [L2 ] doesn't recommend it for those who already know Tcl and similar languages.
lv Would someone consider detailing some of the conceptual differences between PHP and Tcl? What kinds of things will a PHP programmer find confusing or at least different, when learning Tcl?
PHPers want to put in lots of $-s, much as Perlites do, and have less regard for associative arrays than they ought. They often have trouble with Tcl's simplicity.
In a remarkable newsgroup posting [L3 ], Derk Gwen provides a recipe for the C implementation required to link in a Tcl library so PHP source can also interpret Tcl.
See a Tk binding for PHP at [L4 ]
Incidentally, our own SS maintains an attractive "web-based interactive shell for PHP" he and his collaborator call "PHP Interactive" [L5 ].