The stock market's sharp downturn in recent weeks has pulled the three major stocks indexes into what is known as a "correction." [...] when does a market correction effectively end a bull market and usher in a full-blown bear market? HOW IS A BEAR MARKET DIFFERENT FROM A MARKET CORRECTION? A correction is a Wall Street term for when an index like the Standard & Poor's 500 index, the Dow Jones industrial average, or even an individual stock, falls 10 percent or more from a recent high. In the S&P 500, the index that investors pay the most attention to, there have been 19 corrections since 1945, not including the current one, and 12 bear markets, according to S&P Dow Jones Indices. The S&P 500 entered its most recent bear market on Oct.