I will try to explain
Imagine a slow roll. that would be a full 360 degree roll taking say... 4 to 6 seconds to complete. This will require the use of elevator and rudder in a "Blended" or "Transitional" manner. In other words, you are adjusting the amounts of elevator and rudder inputs to maintain a level flight path while rolling slowly.
A rolling circle is a slow roll, or rather 4 slow rolls (Typically 4, occasionally 1 or 2 or 3) done sequentially, but adjusting the flight path such that each 90 degrees of a circle will consist of one roll. You fly a horizontally oriented circle while rolling. Maybe I will do one in G2 while recording and send to you the file?