"The old days" is a phrase that refers to a time in the past, often looked back upon with nostalgia. However, there are many synonyms that can be used to describe this period. "Yesteryear" refers to a time that has passed, often from a bygone era. "Days gone by" is another phrase that is used to describe a time no longer present. "The good old days" often implies a time of innocence, simplicity, and happiness. Other synonyms include "the past," "days of yore," and "days of old." Whether it's "the old days," "days gone by," or "yesteryear," these phrases all capture a sense of fond remembrance for a bygone era.