Most small refrigerators will use whats called a cycle defrost. You can tell these apart from others by a cooling plate in the food compartment. This plate may frost up during running. Because the food compartment is suppose to be 38-40 degrees,the frost will melt when the refrigerator shuts off. The whole interior of the freezer will also frost up. The temp in freezer should be 0-5 degrees so when the frig shuts off the frost remains. This frost needs to be removed but not by scraping or pounding on it. Best way to remove frost is to boil large pot of water and put in freezer and shut door. You can punchure the freon tubes by pounding on or scraping the frost.

Thanks ! Then, if you put a pot of hot water in the freezer, is there a drain that the melted frost disappears through? Or do you have to put sponges or something in the freezer to clean it up with?
I think of defrosting as being a messy job but maybe that was only "in the olden days" when it was not "partially automatic".

Yes there is a drain. Most likely a small hole in bottom near the back and in the center