It looks like it’s Warren Buffett’s turn to say, “I told you so.” Late last year, the Berkshire Hathaway CEO was busy selling stocks when the S&P 500 logged more than 50 record closes, leading many market observers to scratch their heads.

Warren Buffett over the last six decades transformed Berkshire Hathaway ( BRK.A 2.87%) ( BRK.B 2.27%) from a small textile operation into a trillion-dollar company. Under his leadership, Berkshire shares have advanced more than 5,500,000%, crushing the 39,000% return in the S&P 500 ( ^GSPC 1.59%).

Such a precipitous increase in the value of U.S. equities has stirred up the usual cacophony of equity-bears screaming “bubble!” “Bubble” is a popular term, but, as it turns out, is rather ill-defined and fuzzy.