感觉阈限（英语：Sensory threshold）是学术研究中的常用语，指令对象发生某种变化所需的某种条件的值。阈值根据条件本身可以有不同的单位。阈值被广泛运用在包括建筑学、生物学、航天、化学、电信、电子和心理学等各个领域，并作为词根派生出大量的相关词汇。该词与极值没有必然联系。

绝对临界值（英语：Absolute threshold）在心理学中表示人可以感知特定刺激（声音，光，压力，味道，气味）的最小值，低于这个值人就感觉不到特定刺激。

区别临界值（英语：Difference threshold指人可以感知两种刺激之间有区别的最小值， 两种刺激之间的区别如果低于这个值人就感觉不到它们之间是不同的。

In neuroscience and psychophysics, an absolute threshold was originally defined as the lowest level of a stimulus —light, sound, touch, etc.—that an organism could detect. Under the influence of signal detection theory, absolute threshold has been redefined as the level at which a stimulus will be detected a specified percentage (often 50%) of the time. The absolute threshold can be influenced by several different factors, such as the subject's motivations and expectations, cognitive processes, and whether the subject is adapted to the stimulus.
The absolute threshold can be compared to the difference threshold, which is the measure of how different two stimuli must be for the subject to notice that they are not the same.