Sure!
PHP is a sever side scripting (interpreted) language mainly used for the back end of web sites.
It's used as the main server side scripting language on over a third of the world's websites.
It stands for 'PHP: Hypertext Preprocessor' (a recursive acronym
), and it was basically designed to produce html pages & deal with all the business logic & data associated with dynamic & functional websites.
PHP is a runtime language, unlike say Javascript which is asynchrnous & event based, meaning it runs straight through and once it's done you have to call a script again to get it to do stuff.
Also, it's entirely server based.
Here's a link to the PHP Group's site.
You may have heard of a LAMP environment.
That stands for Linux Apache MySQL & PHP, which is basically all you need to build and host websites.
I'm currently running a LAMP enviroment on this machine, and I use it to develop on by setting up virtual hosts using Apache so I can see & interact with the sites I work on in real time without worrying about or dealing with a remote server until it's ready to be uploaded.
Of course, since almost no hosting environment is set up exactly the same as another there are sometimes issues when I take the stuff live, but I'm pretty good at figuring out & fixing stuff like that.
PHP, Javascript, HTML, & CSS are the primary languages used for building websites, or at least that was true for a long time, though it's changing now.
For instance, Javascript used to be purely browser run but with the addition of the Backbone.js and Node.js libraries it's now possible to run it as you main server side scripting language as well, and even use it as a database handler.
Personally I really like PHP.
Its structure & syntax is similar to C & PERL and other languages I've used in the past, it's extremely forgiving, and it boasts an impressive array of functionalities including a command line interpreter which makes it useable as a general server side scripting language for non-web related tasks as well.
Plus there's a really great development community, powerful frameworks, and plenty of online info for when you get stuck or aren't sure of the best way to do something.
Still, PHP has its limitations & strengths like anything else.
That's why I've started to try to learn a bit of Javascript & jquery because of the extremely powerful ability they give you to manipulate the page after it's been loaded, and I'm really interested in learning AJAX as well so I can start doing async script calls, by building a little internal site API using PHP to pass data back and forth from the PHP to the JS & thus the page without having to call other routes directly to run the script.
Sorry if I'm rambling, I get a little caught up sometimes.
Anyhow, I hope that answers your question satisfactorily. 