Circular Journeys are along certain fixed routes with major stations along them - and they have a time validity like 36 days, 52 days etc. You can check out the Northern Rlys ones at http://www.indianrail.gov.in/circularjourney_NR.html
You are allowed a maximum of 8 breaks per journey -- You can come up with your own itinerary, breaking your journey at any station for as long as you want (within the validity of the ticket). They work out much cheaper.
