what is php?

Hypertext Pre-processor: What
is PHP?
What is PHP?
Hypertext Pre-processor (PHPs)
is a server-side scripting
language, and server-sidescripts
are special commands you must
place in Web pages. Those
commands are processed before
the pages are sent from your
Server to the Web browser of
your visitor. A typical PHP files will
content commads to be executed
in the server in addition to the
usual mixture of text and HTML
(Hypertext Markup Language)
tags.
When you type a URL in the
Address box or click a link on a
Web page, you're asking a Web
server on a computer
somewhere to send a file to the
Web browser (sometimes called
a "client") on your computer. If
that file is a normal HTML file, it
looks exactly the same when
your Web browser receives it as
it did before the Web server sent
it. After receiving the file, your
Web browser displays its
contents as a combination of
text, images, and sounds. In the
case of an PHP page, the process
is similar, except there's an extra
processing step that takes place
just before the Web server sends
the file. Before the Web server
sends the PHP file to the Web
browser, it runs all server-side
scripts contained in the page.
Some of these scripts display the
current date, time, and other
information. Others process
information the user has just
typed into a form, such as a page
in the Web site's guestbook
To distinguish them from normal
HTML pages, PHP files are usually
given the ".php" extension.