The term nostalgia describes a sentimental longing for the past, typically for a period or place with happy personal associations. In common, nostalgia sometimes includes a general interest in past eras and their personalities and events, especially the "good old days," such as a sudden image, or remembrance of something from one's childhood.
and when i'm listening to Nostalgia which played and composed by SungHa, it really brought me tears. Reminiscing the good old days and memories. The past, which can only be remembered,but it's no longer here,gone forever.