“Galvanic skin conductance” is a term referring to variations in electrical conductivity which can be measured across the surface of the skin. Changes in conductivity are attributed to changes in the activity of the autonomic nervous system, which, when active, is associated with increased sweat production as well as increases in heart rate and blood pressure, and diversion of blood from gut toward limb musculature (1). Increases in sweat production increase conductivity, and although this does not tell us specifically which emotional response the subject is experiencing, it is at least an indication of levels of autonomic activity. Measurements of galvanic skin conductance are useful for many types of psychological research, and are also used with biofeedback devices in which a subject may want to control responses to stressful situations.
Source: (1) Critchley, Hugo D. (April 2002). “Book Review: Electrodermal Responses: What Happens in the Brain”. Neuroscientist. 8 (2): 132–142.