The most common use of the term in the U.S. investing community is for a statement about earnings that are materially different from the expectation of financial analysts or from prior guidance given by the company.
These preannouncements seem to have become more frequent in the U.S. since the effective date of Regulation FD.
[1] On average, they are made about 20 calendar days before the scheduled announcement or Earnings Call.
The period during which preannouncements tend to be made is sometimes called the "confessional season" because so many of them are bad news.
[4] It has been suggested [5] that potential litigation costs are one reason for announcing bad news early - the company may be at risk of being sued for having known the bad information, not having revealed it, and causing a loss to those who bought stock after the company knew.