noun
whole year; entire year; year-round
Refers to the whole span of a year. In modern Japanese this use is often seen in compound-like expressions such as 周年栽培 or 周年営業; 通年 is more everyday for plain 'throughout the year.'
このトマトは温室で周年栽培されている。
These tomatoes are cultivated year-round in greenhouses.
地域の雇用を安定させるため
They are aiming for year-round operation to stabilize local employment.
noun, used as a suffix
nth anniversary; year anniversary
Used after a number or event name to count anniversaries: 10周年, 創立50周年, 結婚30周年. It marks the anniversary year or occasion, not simply the number of years elapsed in any context.
会社の創立50周年を祝う式典が開かれた。
A ceremony was held to celebrate the company's 50th anniversary.
来月、私たちは結婚10周年を迎える。
Next month, we will celebrate our 10th wedding anniversary.
Counts the ordinal year in a sequence, such as 入社3年目; 周年 is used for anniversaries of an event.
A Sino-Japanese compound of 周, associated with a full cycle or round, and 年, 'year.' The spelling naturally supports both 'a full year' and anniversaries counted by completed yearly cycles.