Means either 'two years' (duration) or 'second year' (ordinal position).
Common patterns
- 二年前: two years ago
- 二年後: two years from now
- 二年間: for two years (emphasizes duration)
- 二年目: the second year (ordinal)
- 二年生: second-year student
Year counting
Years use 年: 一年, 二年, 三年, 四年 (note: 四, not し), 五年.