noun
one year; period of one year
Refers to a duration of one year. Often used with time-related expressions.
彼は一年間日本に留学した。
He studied abroad in Japan for one year.
このプロジェクトは一年間かけて準備された。
This project was prepared over a period of one year.
一年 is a more general term for 'one year' and can refer to a calendar year or a duration, while 一年間 specifically emphasizes the duration of one year.
Compound of 一 (いち, 'one'), 年 (ねん, 'year'), and 間 (かん, 'interval, period').