noun
resuming work after the New Year's vacation; first work of the year
Refers to the first day back at work after the New Year holiday, or the first time one works in the new year. Often used in business contexts.
今日は仕事始めで、久しぶりに会社に行った。
Today was the first day back at work after the New Year's vacation, and I went to the office for the first time in a while.
On the first workday of the year, everyone exchanges New Year's greetings.