Define 'current source.'

A current source is defined as a device that maintains a constant current regardless of the voltage changes that may occur across its terminals. This characteristic makes current sources particularly valuable in electronic circuits, especially in applications where a specific current needs to be supplied consistently, irrespective of variations in load resistance or supply voltage.

In practical terms, a good current source can adjust its output voltage to ensure that the current remains stable even when the connected load changes. This is particularly important in scenarios such as sensor applications, biasing for transistors, and in operational amplifiers where precise current regulation is needed.

While devices that maintain a constant voltage also play crucial roles in electronic systems, they define a different functionality than a current source. Similarly, devices that generate alternating current or those used exclusively in AC circuits do not encapsulate the essence of a current source, which is focused solely on current control. Thus, the definition and functionality attributed to a current source mark it as a crucial element in both theoretical concepts and practical electronic design.