What is an example of an electrical system that uses a parallel circuit?

Most Xmas lights nowadays are wired in parallel. The reason being

if one bulb fails the remaining lights stay on.

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All of the lights in your house are in parallel.

All of the wall-outlets in your house are in parallel.

All of the lights, wall outlets, and everything plugged into the wall,

are all in parallel. They're also most likely in parallel with everything

in the houses of your neighbors on both sides of your house.