years later; after (some) years
Used to indicate a point in time a certain number of years after a reference event. Often follows a number of years (e.g., 数年後, 10年後).
He returned to his country ten years later.
Several years later, the town had changed greatly.
Let's meet at this place again in three years.
We held a reunion ten years after graduation.
年後 (as in 5年後) means 'years later', while 前 (as in 5年前) means 'years ago', giving the opposite time direction.
年後 specifies a number of years into the future, whereas 後日 vaguely means 'at a later date' without indicating how much time will pass.
Compound of 年 (year) and 後 (after, later).