Final answer:
Direct current (DC) is a type of electrical current that flows in only one direction and is typical of a constant-voltage circuit.
Step-by-step explanation:
The constant, even-flowing electrical current that travels in one direction only is referred to as direct current or DC current. This type of current is characterized by the constant flow of electric charge in a single direction, which is a hallmark of the steady state of a constant-voltage circuit. When we discuss systems with a source voltage that is constant, we are typically describing a direct current system. The notion of direct current contrasts with alternating current (AC), where the electric charge periodically reverses direction. In metal wires, current is typically carried by the movement of electrons, resulting in the flow of negative charges. However, in various other mediums such as electrolytes or nerve cells, both positive and negative charges can move.