In relation to the stock market , what is the expression Ex-Dividend date mean ?

Ex-Dividend translates to "without dividend" date. It is a date set by the Uniform Practice Committee or by the specific Stock Exchange. It is a date upon which a given stock will begin trading in the marketplace without the value of a upcoming dividend included in the contract price. It is closely related to and dependent on the date of record. It is often displaced as "X" in the stock listing tables in the newspapers.