A four-character idiom meaning that ten years is a long time and the pace of change makes the past decade feel like ancient history.
IT業界では十年一昔で、昔の常識が通用しないことが多い。
In the IT industry, ten years is a long time; many old conventions no longer apply.
古い写真を見ると、服装や髪型が違っていて十年一昔に感じる。
Looking at old photos, the clothes and hairstyles are different and it feels like a different age.
技術の進歩は早く、十年一昔だと言われることがある。
Technological progress is fast; people sometimes say 'ten years is a long time.'