Voltage sources
A two-terminal element is called an independent voltage source if it maintains a prescribed voltage across the terminals of the arbitrary circuits to which it is connected.
Current sources
A two-terminal element is called an independent current source if it maintains a prescribed current into the arbitrary circuits to which it is connected.
Dependent Sources
A voltage or current source whose source (controlled) variable depends on some other voltage or current in the network (i.e. the controlling variable.
