Wordnet 3.0
NOUN (1)
1. 
 (psychophysics) the difference between two stimuli that (under properly controlled experimental conditions) is detected as often as it is undetected; 
[syn: just-noticeable difference, jnd]
WordNet (r) 3.0 (2006):
jnd
    n 1: (psychophysics) the difference between two stimuli that
         (under properly controlled experimental conditions) is
         detected as often as it is undetected [syn: just-
         noticeable difference, jnd]
V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):
JND
       Just Noticeable Difference (video)