Definition: an “open source” programming language for building dynamic web sites. PHP can be used to write server-side programs that access databases. PHP is the most popular web programming language – more popular than Microsoft’s ASP (Active Server Pages), JSP (Java Server Pages), and Macromedia’s Cold Fusion. PHP is especially well-suited for Web development and can be embedded into HTML. PHP is secure, easy to learn, efficient, fast to code and fast to deploy. PHP is being used by over nine million web sites (over 24% of the sites on the Internet), due largely to benefits such as quicker response time, improved security, and transparency to the end user

FirstClickSEO Commentary: PHP is open source, so there are more people that develop in this language than any other. PHP has few limitations. Perhaps its only weakness is that it’s up against Microsoft’s ASP technology.