A short, brief, or temporary change in the state of a system when there has been a disturbance. The transient effects in a well-controlled system tend to die away with time, allowing the system to settle to a steady-state condition. For example, a thermometer initially reading a temperature T1 immersed in a hot oil of temperature To will read a new temperature of T2:
where τ is the time constant. The exponential term will eventually die away with time to give the steady-state value of the thermometer reading the oil temperature.