Usually the voltage and current sources have the ability to generate specific voltage or current irrespective of any other element in the circuit. So, they are not dependent on any other circuit element and termed as independent sources.
But the sources, whose output (current or voltage) is a function of some other voltage or current at a point in a circuit, are called dependent (or controlled) sources.
Dependent sources are represented by a symbol in the shape of a diamond. The symbol is shown in the figure. In the following table the relationship among source voltage and the dependent voltage or the source current or the dependent current is shown:
