A stock is a security guaranteeing its owner (stockholder) the right to have a share in assets of a joint stock company, in its management and profit, and if the company is dissolved, to have a share in the liquidation balance. A stockholder is entitled to a share in the profit of the joint stock company in the form of a dividend.
The amount of the dividend is decided on by the General Meeting, formed by stockholders (depending on the achieved profit). The dividend amount is variable, which makes a stock different from investments with fixed yield (a term deposit, building saving, bond, mortgage-backed bond).
The stockholder will only become entitled to a dividend if s/he holds the stock on the so-called decisive day. The decisive day is determined by the General Meeting. If a stockholder holds a stock on the decisive day is entitled to get a dividend. Thus a stockholder may hold a stock for one day in a year only to become entitled to a dividend. On the contrary, if a stockholder holds a stock for 11 months, but sells it, and the decisive day is on the day that the trade is settled or later, the stockholder shall not be entitled to a dividend.
Some companies may have set different rules for the entitlement to a dividend. For example, it applies to some companies that it is the day of trade but not the day of settlement that is decisive for the entitlement to a dividend. If a client buys such a company on the decisive day, the client will be entitled to a dividend; if the client sells the company on the decisive day, s/he will not be entitled to a dividend.