A pond is typically a body of water smaller than a lake. However the difference between a pond and an artificial lake is subjective. They are both formed by ponding water, either by excavating a hollow in which water may lie or by forming a dam to impound the water in a valley. The techniques may be combined to form a reservoir in flat country by enclosing an area with an embankment. Such a pond, unless very small, is usually called a reservoir. In some cultures, the meaning has been extended to include small bodies of water impounded naturally. (Oxford English Dictionary)
Scientifically, a pond is any body of water where light is found in the entire body of water. A lake is any body of water that has a profundal zone; there is as limit of effective light penetration for organisms. Hence, Lake Superior can theoretically be defined as Pond Superior because light does extend to the bottom of the "lake".