The word union comes from Latin, specifically it arises from the term “unus” which means “one”. So a union expresses the result of joining something to something else, as well as when a person or groups of people join others. When a woman and a man decide to live together and get married either in the church or civilly, they also speak of a union.

When there are affinities of wills and there is mutual effort, then we will be talking about union, for something there is the saying “in union there is strength”, when people come together for a common good it is much easier to achieve objectives.
To give an example, we have the European Union, which is made up of 27 countries on the European continent that decided to form a political society in order to contribute to the achievement of happiness in all areas: economic, social, etc., of all people who live in those regions.
Economically speaking we find the monetary union, which is nothing more than the merger of two or more countries that reach an agreement where they decide to use the same currency for their commercial transactions.

When a foreign currency is unanimously accepted, we will be talking about an informal monetary union, when a foreign currency is accepted through a bilateral or multilateral treaty, as the case may be, and this in turn is associated with the issuance of its own currency and a fixed exchange system, we will be referring to a formal monetary union. Now, if a group of countries decide unanimously and by common agreement to create a monetary policy and a common authority that legislates the currencies that they are going to share, we will be talking about a formal monetary union with a common policy.
To give an example, we have the so-called euro-zone, where the member countries of the European Union adopted the Euro as their official currency, originating what we previously mentioned: the monetary union.

In turn, we could talk about the so-called customs union, which refers to that area where free trade predominates and where a common tariff has been created, that is, the countries that make up this union determine a common trade policy. With respect to those countries that are not members, this union has as its goal that the partner countries achieve economic efficiency.