El Gobierno – las Cortes - el Congreso
The concept of separation of powers is common in Western countries and is known as separación de poderes or división de poderes in Spanish. The three branches of government are usually referred to as el Poder Ejecutivo (the Executive Branch), el Poder Legislativo (the Legislative Branch) and el Poder Judicial (the Judicial Branch). These three terms will be understood in all of the twenty countries where Spanish is the official language, but different terms are used in the constitutions of some of those countries.
For example, Article 113 of the Constitution of Colombia provides that the government is divided into la Rama Ejecutiva, la Rama Legislativa and la Rama Judicial. In Guatemala, on the other hand, Article 141 of the Guatemalan Constitution refers to them as el Organismo Ejecutivo, el Organismo Legislativo and el Organismo Judicial, while in the Constitution of Ecuador, they are called la Función Ejecutiva, la Función Legislativa and la Función Judicial. The terms used in the Constitutions of Panama and El Salvador are el Órgano Ejecutivo, el Órgano Legislativo and el Órgano Judicial. All of these various terms—poder, rama, organismo, función and órgano—can be translated into English as “branch.”
So far, so good. Where confusion comes into play is in documents from Spain. The Spanish Constitution refers to el Gobierno, las Cortes and el Poder Judicial. This is confusing for two reasons. First, "the Government" in American English usually refers to all three branches of power, but in Spain el Gobierno is the Executive Branch, and the Presidente del Gobierno is the Prime Minister. Second, the term cortes usually refers to the "courts" (and thus suggest the Judicial Branch) in most Spanish-speaking countries, but las Cortes Generales (often shorted to las Cortes) is the name of Spain's Parliament and thus refers to the Legislative Branch. The highest court in Spain is called el Tribunal Supremo (often referred to simply as el Supremo) whereas in Latin America the term more often used is Corte Suprema or Suprema Corte.
Finally, it is important to note that las Cortes Generales (the Spanish Parliament) is divided into two houses: el Congreso de los Diputados (often referred to simply as el Congreso) and el Senado. In the United States the entire legislature is referred to as Congress, so it can confuse American readers if Congreso (de los Diputados) is translated as "Congress." A much better solution is to translate it as the "House of Representatives."