What does "Add Custom Stay" mean in the select a campground section of the Trip Planner?

Sometimes you may wish to stop at a specific location, but you may not choose to stay at one of the campgrounds we have listed from our database.  For example, if you planned to visit family and park at their home, you could add "Aunt Mary's Driveway."  Or you could write down a specific campground not yet in our database.