The term superfood is often used to describe berries, teas, and seaweeds that are either rich in antioxidants, nutrients, or something else that is supposedly better for the body than anything else. Some are just claimed to greatly assist in losing weight such as green tea. There are disputes to many of these claims though. With little to no evidence demonstrating the benefits of antioxidants, some cry out that claiming foods high in antioxidants are better for you is irresponsible. It does not take much use of your imagination to see how the term can be abused. Someone selling a fatty product that wishes to appeal to those who are more health inclined may label their product as a superfood. For example, fatty fish like sardines are often claimed to be a superfood thanks to their oils and high nutritional value. This is not to say that sardines are unhealthy for you in anyway but they may not deserve the label of 'superfood'.
By far, the most popular food to be referred to as a superfood is berries. Blueberries, blackberries, raspberries, and every other type of berry are claimed by many to have properties that improve your health. There is no scientific evidence to support this claim or disprove it to date. This means that calling it a superfood is more or less a baseless claim for the time being. When scientific research indicates that berries do contain health properties above and beyond normal foods then everyone may laugh at how they knew all along. Until then, be wary about anyone claiming something is a superfood.
It would be wise to consult any dietary changes you intend to make with your nutritionist rather than jumping onto any passing fad. Your nutritionist likely knows a thing or two about foods that are good for you and some of them may even turn out to be supposed superfoods.