I'm pretty sure a 'circle trip' is also known as a three city ticket (though it could be more) - starting and stopping in the same place but with stops along the way, but still same itinerary. For example, you fly ORD-JFK on one leg, another leg of JFK-FLL, and then a third leg of FLL-ORD. You'd obviously build this kind of itinerary to spend some time in each location, but can book it is a single itinerary. Your itinerary would thus be:

ORD-->JFK
JFK-->FLL
FLL-->ORD