Edison was not the first to "invent" the incandescent light, there were 23 before him who invented the same thing. While Edison's version might have been superior to the preceding bulbs due to the fact he was able to achieve a greater vacuum inside the bulb, he is known for something he never actually did. When Edison invented Direct Current, or DC, he was angry that the general public saw Alternating Current, or AC, as a safer alternative. How did Edison respond to claims of DC being unsafe? He electrified the stuff out of dogs, cats, horses, and many more animals with high voltages of AC to show that it was "less safe" than DC, which is false.
Think of an electric fence. The current in an electric fence goes off and on many times per second, the current alternates between on and off states. If the current did not alternate, anything that touched the fence would be fried. This non-alternating current is Direct Current. Edison was quite the bullstuff artist.
