Refrigerator and Fridge are the same thing. Fridge is a shortened form of Refrigerator. You can't look at actual definitions here, or you'll come up with the answer that Freezers, Refrigerators, and Chillers are the same thing (Maybe not Freezer). They are all "Things that cool".
You have to look at the implied meaning, or the meaning that everyone takes it to mean. A Refrigerator/Freezer Combo is called a Refrigerator. The colder of those two compartments is called a Freezer. The weaker is (also) called a Refrigerator, although to avoid the awkwardness of saying that there is a "Refrigerator inside a Refrigerator", many people just call it a Fridge. A Chiller is simply a smaller, weaker refrigerator. It is commonly used for wine.
Voila.
P.S.
Chiller#1 http://images.surlatable.com/surlatable/images/en_US/local/products/detail/574210.jpg
Chiller #2 http://lg.electrical-guide.info/images/content/chill/gcw061bxh-lg-wine-cooler.jpg
Refrigerator (Fridge=right, freezer=left) http://www.appliancist.com/whirlpool-super-premium-espresso-refrigerator-20ri-d4.jpg