1. a time in the past when things were better than the present
reminisce about the good old days
When someone talks about 'the good old days' they are referring to a time in the past that they feel was more ideal or better than the present time. This expression is usually used to express sentimentality about the past or used in a sarcastic way to highlight how things are done differently now compared to long ago. You are more likely to hear this used in social contexts.