A current source is a power source that provides a set amount of current no matter what voltage is required to maintain the current. An ideal current source can create an infinite voltage but in reality, the voltage will be limited by the source. While less common than voltage sources, current sources are used in driving LEDs, charging batteries, and in semiconductor circuit design. Do not open-circuit current-sources as they will attempt to create an infinite voltage to overcome that open-circuit.
Supplies I = V/ri to load with ri in parallel.
Grob’s Basic Electronics, 11th Edition by Mitchel E. Schultz