The old days; the past; former times — refers to things or times long ago.
昔は手紙が主な連絡手段だった。
In the old days, letters were the main means of communication.
昔の友達と再会して、当時の話をした。
I met an old friend and talked about the times back then.
昔話を聞かせてください。
Please tell me a story from long ago.
昔の写真を見ると、いろいろ思い出す。
Looking at old photos brings back many memories.
Used as a unit of time in phrases like '一昔' (one decade) or '二昔' (two decades), meaning roughly ten years.
一昔前には今ほどインターネットは普及していなかった。
A decade ago, the internet was not as widespread as it is now.
その流行は二昔前のものだ。
That trend is from two decades ago.