An anode and a cathode are the two types of terminals in an electronic device. The cathode is the terminal where current leaves an electronic device. The anode is the terminal where current flows into an electronic device. Electrical current is the amount of charge that passes a fixed point in one unit of time.
In a standard battery, such as a D-size flashlight battery, the anode is the positive terminal and the cathode is the negative terminal. The anode of a battery is involved in an oxidation reaction. Electrons that reside in the anode are transferred into the electrolyte as a result of this reaction. The cathode of a battery is involved in a reduction reaction. This results in the cathode gaining electrons from the electrolyte. Excess electrons in the cathode are forced out through the circuit and back into the anode. Electrons are negatively charged and are repelled by the negatively charged cathode. The force of this repulsion is called voltage.
In other electronic devices the polarity is reversed. The anode is the negative terminal and the cathode is the positive terminal. The flow of current remains the same. Current always flows out of the cathode and into the anode.