It means a random roster of no pattern at all. You will have days off peppered through your month, you will switch from earlies to lates and you will not be able to predict next month until the 17th of this month.
It is a roster considered so much poorer than than the regular roster, that eJ offered us £10,000 extra to do it for just 3 months recently.
You will also be paid significantly less than anyone else at eJ in Europe. The reason we are recruiting is that no one internal will touch it.