What is a dynamic web page?
As opposed to a 'static' web page, a dynamic web page employs scripting languages to improve interactivity with the user.
There are two kinds of scripting language; Client-side and Server-side.
A Client-side language is usually downloaded with the requested web page and executed by the browser. Iterate uses Javascript and Java Applets to create a software interface for a web page that includes the capability of processing user input or lack of.
A Server-side langauge pre-process a web page on the web page server before the user downloads it into their browser (but after the request for the page is made!). Of its many uses, a Server-side langauge is also distinctly useful for processing the information submitted by users in web page forms. Iterate uses PHP as the backbone for its Content Management Systems.
Why use open source software?
It is free to redistribute.
The source code is freely obtainable and therefore the intent is transparent.
It is the hackers pilgrimage of learning.
A definition of open source software can be found at http://opensource.org/docs/osd