(Reuters) - The S&P 500's .SPX bull market turned 3,453 days old on Wednesday, making it the longest such streak in history, according to some investors' definition.

The market took the milestone in stride, with the benchmark stock index edging 0.04 percent lower a day after it set an all-time intraday high that slightly exceeded the previous one set in late January.

“Length is not necessarily the thing I’m interested in. More so it could be the new high for the year,” said Joe Saluzzi, co-manager of trading at Themis Trading, in Chatham, New Jersey.

Wall Street is widely considered to be in a bull market that started on March 9, 2009, when investors grappled with the global financial crisis that had vaporized over half of the U.S. stock market’s value. Since then, the index has more than quadrupled.

Now after nine years and five months, investors are debating when, not if, the current run-up in stock prices will end.

Bull and bear markets are identified only retroactively, and it is too soon to say for certain whether a correction in the S&P 500 in February marked the end of the bull market and the start of a bear market.

To be sure that the S&P 500 is still in a bull market, it would have to close above its record high set on Jan 26, which it failed to do on Tuesday.

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“That potential new high is important,” S&P Dow Jones Indices analyst Howard Silverblatt wrote in a research note. “(If) we drop 20 percent before we reach a new high, we will go back and declare that the current bull market ended on January 26, 2018, the last high.”

Wednesday’s record is also debatable because Wall Street experts define bull and bear markets differently.

Some experts say a bull market occurred from 1990 to 2000, which would make the current one the longest ever. Others say that bull market started in 1987 and ran to 2000, which would be three years longer than the current bull market.

Apple Inc AAPL.O is responsible for 4.1 percent of the S&P 500's return since March 9, 2009, more than any other company. Microsoft Corp MSFT.O is second, with a 2.4 percent contribution, according to Silverblatt.

(For an interactive graphic on 'The long bull run in context' click here)