"串休“ means Company let you or you volunteer to work on the weekend or holiday，later you can take a rest equal to how many hours you worked in the past. Usually you can choose the day you want to take a rest if you have a good boss or leader,:).

串休 = 振り替え

串休..mean is For example : today should you rest day.but your company tell you .you cant rest today you need work.....and they changed your holiday to tomorrow or the other day.. " sorry my poor english ... "