This week's turmoil in European and Asian share prices has prompted some analysts to talk about a bear market.
The last bear market was after the 'dot-com' bubble burst in 2000
But what exactly is this strange phenomenon, and how does it differ from the bull optimism that has gripped markets over the past couple of years?
One common definition of a bear market is that stock indexes need to fall 20% from the market's recent peak.
According to some reports, more than 40 global stock markets are already there, and there are fears of more declines.
"Riveted by recession worries in the US and fearing a slowdown, Asian and European stocks have been severely impacted," said Stephen Pope, chief global strategist at Cantor Fitzgerald.
"Europe is already in a bear market," he said.
On Monday, European stock indexes chalked up their biggest daily loss in years as fears of a US recession unsettled investors.
"I think we can safely say that the stomping, snorting optimistic beast of a market is fleeing the field, to be replaced by something scary and grizzly," said the BBC's business editor Robert Peston.
But if you look at individual stock markets, the picture is not quite so clear.
France's leading index, the Cac 40, is down by more than 20% since a peak in June, shares in Milan and Madrid are very close to that sort of loss.
Japanese and Chinese shares have been experiencing a bear market longer - they broke the 20% barrier late last year.
But shares in London and Frankfurt are not down that far yet.
In the US, the benchmark Dow Jones industrial average is down 15% from its high, hit in October 2007.
But not all analysts believe the term "bear market", or its counterpart "bull market", is useful.
"People get very excited about whether we're in a bull or bear market, but frankly I think it's irrelevant," said Bob Parker, deputy chairman of Credit Suisse Asset Management.
"The first quarter and second quarter will be difficult. We're in the danger zone now but historically speaking, the market is looking cheap."
Karen Olney, chief European equity strategist at Merrill Lynch, says the markets are at a turning point.
"From here, if there's a profits recession, then we could go down another 10%," she says.
"But, if it's just a mid-cycle slowdown, then it could be a great buying opportunity."