adverb
Describes something that happens or is done once each year.
このイベントは年ごとに開催されます。
This event is held annually.
年ごとに新しい目標を立てる。
I set new goals every year.
毎年 is the most common word for 'every year' and is more neutral; 年ごとに emphasizes the repetition per year and can sound slightly more formal or written.
年々 means 'year by year' and focuses on gradual change over years, while 年ごとに simply means 'each year' as a discrete event.
Compound of 年 (toshi, 'year') + ごとに (goto ni, 'each, every'). The ごとに part derives from 毎 (goto) + particle に.