When a switch is closed in an electrical circuit containing a capacitor or inductor, the component draws out the resulting change in voltage or current, causing the system to take a substantial amount of time to reach a new steady state. This period of time is known as the transient state.
A capacitor acts as a short circuit immediately after the switch is closed, increasing its impedance during the transient state until it acts as an open circuit in its steady state.
An inductor is the opposite, behaving as an open circuit until reaching a short circuit steady state.