Nostalgia (from classical Greek νόστος [nóstos], “return,” and ἄλγος [álgos], “pain”) is a feeling of sadness mixed with pleasure and affection when a person thinks of times considered happy in the past, also described as a feeling of longing for a past moment, situation, or event. It is commonly referred to as a feeling that anyone can go through at any biological stage, for it is the suffering caused by thinking about something that one had experienced at some stage in the past and is no longer available or has changed radically.