Our material body is our visible, physical identity in the material world. It is made of material elements—solids, liquids, gases, etc.—and exists for a limited time. It is born, grows to maturity, and produces offspring; it then gradually dwindles, ceases to function, and ultimately vanishes.
What we call a "living body" is a combination of two kinds of energy—material and spiritual. Material energy supplies the gross materials of which the body is made, and spiritual energy animates the body and enables it to work. Without the presence of a spiritual spark—the self or atma—no material process can give life to the body.
We tend to identify ourselves as our material body. If our material body is male, female, old, young, black, or white, we think we are male, female, old, young, black, or white. This misconception, called false ego, is at the root of most of our anxiety. Because of false ego, we believe "death" means the end of our existence, when it's actually just the end of the material body's existence. We're not the material body. We're spiritual.