“Whisper numbers, according to Wikipedia, emerge from widening cracks in the spreadsheets maintained by Wall Street analysts,” Phillip Elmer-Dewitt reports for Fortune. “‘”When the estimate is first calculated by sell-side analysts, the number is submitted to companies such as First Call to be averaged with other analysts’ estimates for the consensus earnings estimate. As new information is made available and plugged into the spreadsheet, the calculation may change several times leading up to a company’s actual earnings release. However, the analyst is generally not going to issue a new report and revise his or her published estimate with each new calculation, resulting in the analyst’s true expectations differing from his or her published number. Therefore, when someone within the firm, an institutional client, or even a retail client asks the analyst his or her expectation for the company, the response is often different than the published estimate. This number then gets passed among trading desks and professional traders as the whisper number.'”
Full article, with the averages of the six analysts — institutional or independent — whose revenue and earnings estimates were closest to the mark over the past four quarters, here.