Entropy/ˈentrəpi/ Definition 1 of 3Pro Tip 1/3Isolated Systems Entropy increases in isolated systems where energy isn't added or lost. The universe is the ultimate isolated system, with entropy always increasing. Pro Tip 2/3Not Reversibility High entropy means a system isn't easily returned to its prior state. Melting ice cubes show increasing entropy as they won't reform without energy. Pro Tip 3/3Order to Disorder Entropy shows a system's transition from order to disorder. A neat room becomes disordered over time, demonstrating entropy.