the time required for the current or voltage in a circuit to rise or fall exponentially through approximately 63 per cent of its amplitude
time constant in American English
noun
Electricity
the time required for a changing quantity in a circuit, as voltage or current, to rise or fall approximately 0.632 of the difference between its old and new value after an impulse has been applied that induces such a change: equal in seconds to the inductance of the circuit in henries divided by its resistance in ohms
Word origin
[1890–95]This word is first recorded in the period 1890–95. Other words that entered Englishat around the same time include: blip, historicism, neoclassicism, plein-air, pogey