In my opinion, a smoothie is just an amazingly tasty drink. However, you may want a more descriptive definition of what a smoothie truly is. It is typically defined as a beverage made of blended fuit and vegetables. Usually it will contain fruits, vegetables, some form of liquid and some type of frozen ingredient. Liquids can be milk, water, yogurt, etc. And the frozen ingredients can be ice, ice cream, frozen yogurt, frozen fruits and vegetables, etc.
One of my favorite aspects of smoothies is the fact that you can add nearly anything you want. If you think that it would taste great, try it. It may take a couple of tries to get the recipe and flavor that you really desire, but the options are endless.