Definition of 'Whisper Number'
1. Traditionally, the unofficial and unpublished earnings per share (EPS) forecasts that circulate among professionals on Wall Street. In this context, whisper numbers were generally reserved for the favored (wealthy) clients of a brokerage.
2. A company's forecasted future earnings or revenues according to the collective expectations of individual investors. In this sense, a whisper number would be compiled by a website polling its visitors. Individuals come up with a whisper number using their own analyses of company financials, market trends, gut feel, etc.
Investopedia explains 'Whisper Number'
Whisper numbers are especially useful when they differ from the consensus forecast. They can be used as a tool to help spot (or avoid) an earnings surprise (or disappointment). Of course, this is only relevant if they are more accurate than the consensus estimate, and this depends on the sources used to calculate them.
Increased regulatory scrutiny on the brokerage industry made it much more difficult (if not impossible) to get a whisper number in the traditional sense. For example, regulations like Sarbanes-Oxley provided for stricter rules in how companies disclose financial data. Employees, financial professionals and brokerages face significant penalties if they provide insider earnings data to a select group of people. While it's impossible to know the extent to which whisper numbers still circulate among the wealthy, it's highly unlikely that a small investor could access this data. For these reasons, the newer definition (expectations of individuals) is of more relevance to regular individual investors.