Declaration date or date of declaration is commonly known as the date the company's directors meet to vote for issuing a dividend.
Those company's directors will declared the amount of dividend, ex-date, record date, and payment date for the dividend. Hence, it is also referred as announcement date. If the payment is authorized, the dividend is known as a declared dividend and it becomes the company's legal liability to pay the dividend to the shareholders.
On the other hands, for options, declaration date serves another meaning - declaration date or date of declaration for option is the last day on which the shareholders of an option are allowed to exercise the option. Hence, it is also referred as expiration date for option.After the declaration date or date of declaration date for option, those options will become useless and are not allowed to exercise anymore.