Basically, pierogi are dumplings with a filling inside of them. There are a variety of fillings that can be put inside the dumplings. A few examples are meat filling, farmers cheese, mashed potatoes together with cheese, or fried onions. The pierogi that I make are filled with large curd cottage cheese. There are also many different names that folks call these little dumplings. I have learned over the years that pierogi is plural for more than one dumpling, and pierog is one dumpling. Some other names, just to mention a few are, pirogi, perogi, perogie, pierogy, and perogy.