Just Noticeable Difference (JND) is the smallest perceptible difference between two stimuli. It is a crucial concept in psychology and physiology. There are several synonyms for JND, including difference threshold, noticeable difference, differential threshold, and minimum difference. These terms are used interchangeably to describe the minimum change in a stimulus that can be perceived by a human being. The JND is essential in measuring sensory sensitivity and determining how much change in stimuli is required for a person to detect a difference. It applies to all senses, including sight, taste, smell, hearing, and touch. The study of JND is vital in understanding human perception and how it affects behaviour and decision-making processes.