A 'module' is simply a piece of self-contained code that handles a specific type of content or performs a specifc type of task.  Each module contains its own presentation code to be able to render its content in a professional, clean look without any programming knowledge from the content author.  This separation of content and presentation allows the author to only have to worry about what they want to present to thier visitors; RCMS handles the rest.  It also allows non-technical people to quickly and easily create professional looking websites without any programming or technical assistance from a 'webmaster'.

Normally, a collection of 'modules' are placed together to create a single webpage.