PHP (PHP: Hypertext Preprocessor) is a reflective programming language originally designed for producing dynamic Web pages. PHP is used mainly in server-side application software, but can be used from a command line interface or in standalone graphical applications. (From Wikipedia)

Basically, PHP is a programming language to create dynamic web pages and web applications that are run on a server and accessed through your browser.
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php is a server-side scripting language used commonly for content, forms, forums, chatting, etc. you can find info here: http://www.php.net and scripts here: http://php.resourceindex.com/
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php is a database langauge it is the magic of puttin somthing in a search box on a site hitting submit and getting a result
to get a little technical it is just a HTML like code but more concetrated and in database form

for example when you type in a phrase or question in the search box and hit submit , it sends a "query" and code gets executed and the program looks for matches and you get a result page

Now to be honest PHP is not the only database langauge out there….
there are quite a few
there is ASP which is made by Microsoft and then theres Perl, AJAX ,Ruby and CGI
They all perform the same function (Data Storage ,Retrieval and other database functions) , they just go about doing it in different ways and not to mention it is coded different
Think of it this way its all ice cream just different flavors
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