The term "perceived" refers to the subjective experience or interpretation of a stimulus by an individual's senses and cognitive processes. It involves how individuals interpret and make meaning out of sensory information.
A threshold is a dividing line between what can be perceived or detected and what cannot. It represents the minimum amount of stimulation required for perception.
The difference threshold (also called just noticeable difference) is the smallest amount by which two stimuli must differ in order for an individual to perceive them as different.