Entropy has previously been investigated from the versatile aspects related to the role of the second law of thermodynamics. In this paper an alternative interpretation of the entropy is presented. A comprehensive explanation of entropy, from classical thermodynamic understanding to a specified quantum model system, is described to introduce another interpretation of entropy. We deal with two model systems. Thery are the Einstein lattice harmonic oscillation model and an ideal monatomic gas model. The main subject is an introduction of statistical thought of thermal average of the Heisenberg uncertainty product between position and momentum. The entropy is defined by incorporating quantum consideration of the uncertainty product. The thermal average of uncertainty relation is embedded inherently into the entropy. The entropy can play a role of a measure of uncertainty product. In the last decade, the relationships between the entropy and the thermal average of uncertainty product have been investigated in a few physical systems. A brief survey of the recent researches is presented. The fundamental role and function of the uncertainty product is discussed from a conceptual view point of complementarity.