darlington pair
Both designations, that of the Darlington transistor as well as that of the Darlington circuit are correct because it is an electronic component or an electronic circuit that works with a pair of transistors. If both transistors are in one package, it is called a Darlington transistor.
The Darlington transistor is a series connection of two transistors. The emitter of the first transistor is connected to the base of the second. The control current thus passes from the base of the first transistor via its emitter to the base of the second transistor. This multiplies the current gains of both transistors to a total gain "V", which is the product of V1 multiplied by V2. In addition to the enormous gain, which can reach values of over 10,000 times, the Darlington circuit is characterized by a high input impedance because of the low base current of the first transistor. MOSFETs have similar characteristics.
Darlington circuits, named after their inventor Sidney Darlington, are suitable for switching large loads with low control power. Thus, Darlington power circuits can switch powers of several 100 W.