What is the Good Neighbor Policy?
I have no disagreement with the above answer, but I'd just like to put it in different words in case that would be helpful.
Before Franklin Roosevelt's presidency, the US intervened militarily in Latin America whenever it wanted. The US sent military units to occupy countries such as Nicaragua and the Dominican Republic when they seemed to the US government to be unstable. Our "right" to do this was set out in the (Theodore) "Roosevelt Corollary" to the Monroe Doctrine. This essentially said we had the right to intervene in any Latin American country if we thought it was not being well run.
When FDR became president, he decided that Latin American countries should be left to control their own affairs, even if they seemed to be doing a bad job of it. This was the Good Neighbor Policy.
Franklin Roosevelt advocated the use of cooperation and trade when it came to improving contact with Central and South America. This route was preferred over the exercise of military strength in order to keep the peace. The notion of the "good neighbor," refers to how if one were to respect themselves, then they would act accordingly toward others. This idea was conveyed to the masses in Roosevelt's inaugural address in 1933.
Another way one could put it- the golden rule. The golden rule has been noted as, “Do unto others as you would have them do unto you.” These ideas of respecting yourself and respecting others in the same manner would ensure a proper code of conduct for all to follow. It would not allow for the hasty intervention of one country in the affairs of another country.
The Good Neighbor Policy was FDR's diplomatic approach to Latin American nations. Previous presidents had sought to influence or maintain control over Central and South American areas to hinder European influence and competition there (Monroe Doctrine, et al), and Roosevelt felt this was all the more important as more and more groups sought independence.
Instead of military control, the Good Neighbor Policy sought to keep peace by encouraging and promoting economic development and self-government. Channels were established whereby developing nations could borrow money for infrastructure and secure assistance in running elections and establishing a government that would have positive ties to the United States from its inception.