In finance, "short selling" or "shorting" is the practice of borrowing shares of stock and immediately selling them in hopes they will decline in value, allowing you to repurchase them later at a lower price, repay your debt (of stock), and walk away with a profit.
More generally, one who stands to profit from the decline of an asset is said to have a "short position" on that asset, or to be "short [the asset]". Analogously, a "long position" is one that rises with the underlying asset. If Sally owns a lot of gold, one might say "Sally is long gold," since she stands to profit from gold increasing in value.
What is the origin of these terms? I assume that "short sale" came first, and "long" was just the natural opposite, but why was the word "short" used in the first place?