Eating foods in moderation is a key to maintaining a healthy diet. That means you have a little bit of everything, rather than gorging, say, on steak and ice cream.
The word moderation describes a middle ground often in either behavior or political opinions. When a politician tries not to be too extreme to the left or right, he is using moderation to hold a middle ground in the hopes of getting as many voters as possible. Moderation can also be the act of tempering an extreme. Try a moderation of your coffee habit, and cut down from 8 cups a day to 2.