'Frost Free' is the latest technology for fridges, what it means is that the refrigerator or fridge will maintain a constant temperature in the freezer compartment and this ensures that the freezer will not build up to with ice.
'Cyclic Defrost' refrigerators are older technology, they do not have a regulated temperature control, therefore frost builds up in the freezer section. They also lack the ability to defrost themselves in these situations. With the build up of ice in the freezer, ice will build up in the freezer section of the fridge.
When this occurs in the Fridge Freezer section you then have to defrost the freezer manually every couple of months. This has disadvantages, as the ice builds up in the freezer it decreases the freezer compartment capacity meaning less storage space.