noun
working on a rescheduled day off
Refers to working on a day that was originally a day off, after that day off has been moved to another date. Common in workplace scheduling contexts.
祝日が土曜日と重なったため、月曜日が振替休日となり、その分の振替出勤はなかった。
Because the national holiday fell on a Saturday, Monday became a substitute holiday, and there was no make-up workday for it.
会社のカレンダーで振替出勤の日を確認してください。
Please check the company calendar for the rescheduled workday.
A substitute holiday (day off) given in place of another day; 振替出勤 is the opposite—working on a day that was originally a day off after moving that day off elsewhere.
Compound of 振替 (ふりかえ, 'transfer, rescheduling') and 出勤 (しゅっきん, 'going to work, attendance').