What do you understand by the …

An open economy is one, which is not only involved in the process of production within its domestic territory but also can participate in production anywhere in the rest of the world. An open economy involves itself in the following activities.
It buys shares, debentures, bonds etc. from foreign countries and sells shares, debentures, bonds etc. to foreign countries.
It borrows from foreign countries and lends to foreign countries.
It can send gifts and remittances to foreigners and can receive the same from them.
Normal residents of an open economy can move or be employed and are allowed to work in the domestic territory of other economies.
Due to these reasons, Gross Domestic Product and Gross National Product are not same in an open economy. It is to be noted that at present all economies of the world are open economic.