noun
1. : the time required for a current turned into a circuit under a steady electromotive force to reach to (e-1)/e or 0.632 of its final strength (where e is the base of natural logarithms) ; specifically : the ratio of the inductance of a circuit in henries to its resistance in ohms
2. : the relaxation time in the discharge of a capacitor that is equal to the product of the resistance in ohms of the discharging circuit and the capacity in farads of the condenser