Last year (the year before the current one). Commonly used in speech and writing. Note: an old/obsolete reading is 'こぞ'.
去年、日本へ旅行しました。
I traveled to Japan last year.
去年と比べて売上が増えた。
Sales increased compared to last year.
去年の冬は例年より暖かかった。
Last winter was warmer than usual.