Direct current (DC or "continuous current") is the flow of electricity in a single direction, from the negative to the positive terminals (potential, poles).
The direct current always flow in the same direction, distinguishing it from the alternating current (AC). Direct current used to be called "Galvanic current".
Batteries are some of the main sources of direct current (DC), but many other sources also exist such as bridge rectifiers in power supply, solar panels, etc.