The word "black back" is usually used to describe a person who has been burdened with heavy responsibilities, burdens or difficult missions for a long time, resulting in mental or physical state becoming emaciated or overwhelmed. This word can mean that a person is still tenacious and brave in difficulties and obstacles, but it also expresses the hardships and sacrifices he has made. It can also be used to describe the touching historical imprint left by a region and a nation after wars and disasters.