The "Just Noticeable Difference" (JND) refers to the smallest change in a stimulus that can be detected by a person. This concept is important in fields like psychology and sensory perception, as it helps to understand how we perceive changes in our environment. For example, if you are holding a weight, the JND is the minimum amount of weight added that you can feel. JND varies depending on the type of stimulus and the initial intensity. According to Weber's Law, the ratio of the JND to the original stimulus is constant. This means that larger stimuli require a greater change for the difference to be noticeable, while smaller stimuli need only a slight change.