A share is said to be ex-dividend, from the Latin for "without," when it trades without the right to receive the most recently declared dividend. Anyone who buys the share on or after the ex-dividend date will not get that payment; it goes instead to whoever owned the share before that date. Stock quotes often flag such shares with an "x" or "XD" marker.
How ex-dividend relates to the ex-dividend date
The timing rules, including how the exchange sets the date and how it lines up with the record date under T+1 settlement in the United States, are covered in the main entry on the ex-dividend date. In the dividend timeline, the board first fixes the declaration date, the share then goes ex-dividend, and the cash is paid on the dividend payment date. From an accounting point of view, going ex-dividend changes nothing on the issuing company's books: the liability for dividends payable was already recorded on the declaration date. For investors, the share price usually falls by roughly the dividend amount when the stock opens ex-dividend, because the buyer is no longer paying for that cash. A $50 share paying a $1 dividend would, other things equal, open near $49. Investors who hold shares as investments recognize dividend income based on their entitlement, not on when the cash lands.