1) The degree of stimulation, or electrical depolarisation, necessary to produce an action potential in a nerve-fibre (see NEURON(E); NERVE). Stimulation below this level fails to elicit a conducted impulse, and supramaximal stimulation will elicit the same response as a threshold stimulus.

2) The level at which action needs to be taken based on balancing risks and benefits; thus a doctor would have a low threshold for giving antibiotics to an immunosuppressed person with a fever, but a high threshold for prescribing anything to a woman in early pregnancy.