This is the formal and public disclosure of a pending M&A deal. Prior to announcement, there may be rumours in the market about the deal and even leaks, but they have not been confirmed.
The announcement is usually done through a press release and perhaps a press conference where the chief executives of the purchaser and often the target (if the deal is friendly) are available for questioning by journalists and market analysts.
If the company is listed on a stock exchange, the exchange will also need to be informed on announcement day and, depending on the deal, other regulators may also need to be notified. In some countries, the announcement date marks the time when the regulatory acquisition process starts, which determines when other items, such as the formal offer document, must be provided by the bidder.
The announcement date is when then bidder usually confirms that it will make a formal offer for the company; it is usually the same date on which the deal becomes public knowledge, but in some countries buyers can indicate that they intend to make an offer without making the formal announcement.
For example, the American businessman, Malcolm Glazer, first made public his ownership of over 3% of Manchester United Football Club in September 2003, yet he did not make a formal announcement of his intent to purchase 100% of the club until May 2005, by which time he owned over 76% of the club’s shares.