A black swan is a rare, unpredictable event that can have serious implications for an economy and investing markets.Finance professor and Wall Street trader Nassim Nicholas Taleb popularized the term in his writings. The rise of the Internet, the Sept. 11 attacks and World War I were all black swan events. Black swan events are random and unexpected. For example, the Russian government’s debt default caused the failure of Long Term Management, a previously successful hedge fund. The default was a black swan Long Term Capital Management’s computers could not have predicted. Election results and oil prices have predictable impacts on financial markets, but natural disasters, prolonged conflicts and other black swan events can change things and render plans useless. For example, World War I wasn’t supposed to last anywhere near four years, but it did, and it had serious repercussions for economies across the world. Some analysts claim market predictions are at the mercy of black swan events because no model can account for the unpredictable. They encourage investors to expect a black swan, and to construct portfolios that brace for its impact by using reliable strategies such as diversification, rebalancing and so on.