In finance, betting that a stock price will fall by borrowing and selling shares; or in electricity, creating an unintended direct connection that causes problems.
From 'short' meaning to fall short or be deficient. Financial usage emerged in the 1600s-1700s with stock markets; electrical usage from the 1800s with electricity.
Short-sellers are controversial because they profit when companies fail, but they also catch fraud—short-sellers discovered the Theranos fake-blood-test scandal before regulators did.
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