Wall Street loves its jargon and perhaps no two phrases are more ubiquitous than the bull and bear market. But when Wall Street traders say the stock market is teetering on the brink of a bear market, what exactly do they mean?

The general consensus among investors is a bear market occurs when a major index such as the Dow Jones Industrial Average, S&P 500 or the Nasdaq falls 20% from its previous high.

“What happens in a bear market is everyone stops buying and the mood among investors becomes overtly pessimistic,” said Ryan Detrick, senior technical strategist with Schaeffer’s Investment Research.

The Dow hit an all-time high of 14164.53 on Oct. 9. If the index closes below the 11331.62 level on Tuesday it would indicate the stock market is in a bear market based on Dow Industrial stocks. The broader S&P index, which hit a high of 1565.15 on the same day, would have to close below 1252.12 to enter a bear market.

The criteria for entering a bear market is clear. But coming out of one is a bit more complicated.

Not every bear market is the same. The bear market that led to the decade-long Great Depression ran from 1930 to 1932, while high energy prices and stagflation caused a milder, but much more prolonged bear market in the 1970s.

There’s no general consensus for what turns a bear market into a bull market. While some traders say a bull market starts when an index rises 20% from a tested low, that’s not the general rule. Like many things on Wall Street, it's purely psychological.

“In order for us to move back into a bull market, we need optimism or a belief that prices can only go higher,” Detrick said. “None of the indicators show anything close that's remotely optimistic in stocks at the moment.”

The common denominators of bear markets are higher volatility than usual and stock gains only in very specific industries.

“Energy is going to be big this time around, while everyone knows the financials need to go through a serious retrenching before we’ll see gains there again,” said Frank Haines, chief investment officer at Christian Brothers Investment Services.

Investors said the best thing to do in a bear market as an individual investor is to sit tight and not trade heavily.

“In a bear market people get killed because they keep trying to pick bottoms,” Detrick said. “We’ve seen that in the financial sector, and we saw that with dot-coms during the 2000 bust.”

Another mistake often made by individual investors during a bear market, according to some financial experts, is trying to offset losses by pulling money out of IRAs and 401(k)s, and putting it into bonds or safer money market funds.

While Haines said it’s smart to consider adjusting your portfolio to include more bonds, money markets or other bear market resistant investments, individual investors should avoid going in and out of the market during a bear market and instead weather the storm.

“Even the most savvy of investors can’t pick market tops or market bottoms, so don’t try it,” he said. “Rebounds off bottoms occur very sharply. Just follow a disciplined approached to investing and hang tight.”