A popular server side scripting language. It's perfect for simple applications that shouldn't really even require a user downloading a program (displaying them in the form of webpages instead). The base syntax is similar to c++ but the language is very loose and doesn't require declarations or things like that (which works okay as it is just a scripting language).
The best way to learn the language is probably to dwell through the PHP Manual which is filled with examples and useful functions.