What is the defining characteristic of direct current (DC)?

The defining characteristic of direct current (DC) is that it flows in one direction only. This unidirectional flow of electric charge means that the electrons move consistently from the negative terminal to the positive terminal, creating a steady and straight-line current. This is in contrast to alternating current (AC), which periodically changes direction, resulting in an alternating flow of electrons.

While some forms of DC can operate at a constant voltage, it is not a defining characteristic because variables like load can cause voltage to fluctuate. Additionally, the ability to be transformed into different voltages is a characteristic of AC; DC is typically not transformed in the same way due to its constant directional flow. Thus, the key point in understanding direct current is its one-way flow of electricity, which is what distinguishes it from other types of current.