What is a free modular layout

It is a modular layout with minimal rules The main guidelines are the end where it connects to other modules. There are track and radius limitations so that they will all work together. http://www.utahfree-mo.org/ is the Utah group. I wanted to use my HO scale trains and didn't have a layout. I have decided to build a mini version. My sections will be no more than 18" wide. Most will be 12. It will give me something to run my HO trains on.