Indicates that something happens or is done once each year, on a yearly basis.
In this town, a festival is held every year.
The contract is renewed annually.
年ごと has the same meaning but uses the native Japanese reading とし. 一年ごと is more explicit with the number.
Standard spelling using the suffix ごと.
Kanji spelling using 毎; less common but still seen.
Compound of 一年 (one year) and the suffix ごと (every). The suffix ごと attaches to nouns indicating time or units to express 'every ~'.