This refers to adding a custom position via module manager

This is the ability to create your own position by typing a new position name in the module position box. This enables the ability to load a position in an article using the loadposition plugin syntax - a very useful tool in Joomla

www.joomlabamboo.com/blog/tutorials/using-the-loadposition-plugin-to-load-joomla-content

This picture is an example of creating a position called accordion