But in order for electricity to do its thing, it must travel through a circuit. You can think of a circuit as a pathway through which electricity can travel. In a wall outlet, there is also a positive end and a negative end the two holes into which the two prongs of a plug fit. In the early days of electricity, when Thomas Edison was busy working on his lightbulb, all circuits were simple and generally followed a straight-line path. These types of circuits are known as series circuits, and are the same systems used by most holiday tree lights.
Many circuits can get really complicated.
There are parallel, switched, integrated, and fused circuits.