I saw this asked so many times so i guess it's time there is a place to link too :)
Here is the answer from the one that started it all (Rasmus Lerdorf
[rasmus@php.net]) :
"The first thing I put out was a collection of cgi scripts collectively known as the
Personal Home Page Tools. These were tools I was using on my own home page to track
hits on my resume, do custom logging to mSQL and other things.
I had another tool that wasn't really part of the package that I used to process
form data. Because I am a lazy sod, I kept the filename short. It was just "fi" in
my cgi-bin directory. I sat down and completely rewrote the parser behind the PHP
Tools and at that point it became very obvious that the little FI tool needed to be
an integral part of the package. That's where the whole concept of bringing form
variables directly in and making them available to all the different tools came
from. When talking to people I described it as PHP/FI a couple of times
as a bit of a joke (because it looked like TCP/IP) and it just stuck. I couldn't
think of a better name and people were starting to use it, so I just left it.
When the development team grew and the next rewrite hit (PHP 3) it was decided to
drop the rather awkward /FI part and just make it PHP, but since even at this time
it had grown to be significantly more than a set of tools for personal home pages,
that meaning was also dropped. A name vote ensued and all the proposed names
sucked, so this PHP: Hypertext Preprocessor name was deemed to suck the least. So
that's where we are.
As far as I am concerned PHP is just PHP. It doesn't stand for anything."
-Rasmus
Other associations for PHP :
* People Hate Perl
* Professional Hypertext Preprocessor
* PHP Hypertext Preprocessor