Sentence:  The S&P 500, as of Wednesday, is now in the longest-running bull market ever, as some strategists measure it. That would be one day older than the 1990-to-2000 <WSD>bull run</WSD>, which ended with the bursting of the tech bubble in 2000. 
Meaning of the word marked with <WSD> tags:  A contiguous period during which a stock market is a bull market.