Question

what is frequency of DC

Answer 1

The term DC is used to refer to power systems that use only one polarity of voltage or current, and to refer to the constant, zero-frequency, or slowly varying local mean value of a voltage or current. For example, the voltage across a DC voltage source is constant as is the current through a DC current source.

Answer 2

The term DC is used to refer to power systems that use only one polarity of voltage or current, and to refer to the constant, zero-frequency,or slowly varying local mean value of a voltage or current.
For example- The voltage across a DC voltage source is constant as is the current through a DC current source