PHP is a server-side scripting language designed to be simple and cross-platform compatible.
Web pages incorporating PHP can be transferred from the Windows environment to the Unix environment without change. It is 'open-source', which effectively means it is freely available. PHP currently offers some, but not complete integration with Microsoft COM and Java COBRA components.

It is a 'loosely typed' language similar in syntax to JavaScript, with built-in functionality that is similar to ASP and Cold Fusion. PHP is declared to be cross-platform and can be used on machines running Unix, Windows or Mac. Like ASP, it can be 'embedded' into HTML code, however, unlike JAVA, it is a 'scripting code' rather than a programming language. Whereas you can write a stand-alone programme in a language like JAVA, you cannot do so with PHP. It is 'interpreted' rather than 'compiled'.

PHP is declared to be the fastest growing web scripting language. It is extremely popular with web-developers that are running Apache/Unix servers. Note the emphasis on 'scripting-language' rather than programming language. It is important to differentiate between the two.

Its main advantage is the fact that it works well with Unix/Apache and is relatively fast and simple. PHP has been declared as being easier to learn and easier to implement than other web-development tools such as JSP and ASP.

However, as a 'scripting language' PHP does not have the robustness of ASP or JSP and does not integrate with the COM or J2EE architecture, to any great degree.

Simply put, PHP is fine for generating 'lightweight' web applications, which require minimal business logic. However, it does not do many of the things that JSP/JAVA and ASP/COM are capable of. Nor does it have the weight of Sun or Microsoft behind it as JSP and ASP (particularly .NET) do.

Whereas JSP and ASP are 'industrial strength', it could be said that PHP is designed to offer a more 'lightweight' solution to server-side scripting.