Direct current is defined as the flow of electric charge in:

1. Current sources differ in whether the direction changes. 2. Circuits may run on direct or alternating current. 3. Direct current, abbreviated DC, is the flow of electric charge in only one direction. 4. Batteries are the familiar constant-voltage source. _Source: OpenStax College Physics for AP Courses 2e (CC BY 4.0), Ch 20 'Electric Current, Resistance, and Ohm's Law', sections 20.1-20.7_