What is "concert of europe"

Concert of Europe \Concert of Europe\, or European concert \European concert\ An agreement or understanding between the chief European powers to take only joint action in the (European) Eastern Question.

The Concert of Europe, also known as the Congress System or the Vienna System after the Congress of Vienna, represented the balance of power that existed in Europe from the end of the Napoleonic Wars (1815) to the outbreak of World War I (1914).