The article discusses the evolution of the concept of entropy over 200 years. Initially conceived by Carnot and Clausius in thermodynamics as a measure of unusable energy and decay (the second law), it was later defined by Boltzmann using probability as a measure of disorder. Shannon linked it to information theory, quantifying uncertainty. Modern physics, influenced by Jaynes, increasingly views entropy as subjective and observer-dependent—a measure of ignorance about a system's microstate rather than an intrinsic property. This perspective connects information, energy, and the limits of knowledge, fueling research into information engines, quantum thermodynamics, and the fundamental nature of time.