As you probably know already, AC means alternating current, and DC means direct current. Lest you think there's anything conceptually complex about this, there isn't. The difference between AC and DC couldn't be simpler:

DC means the voltage in a circuit is steady and essentially unchanging, and so the current flows in one direction, as it does with our battery.

AC means the voltage and current in a circuit are forever bouncing back and forth. The current going in one direction, then turning around and going in the other direction, and back again, over and over. As with our sine wave, or any other audio signal, or the much higher voltage sine waves coming out of your electrical outlets.

Just in case there is any ambiguity about this, in the video below I plug the battery into the oscilloscope so you can see its just a steady, unchanging voltage.