Shift work
Shift work is a pattern where the hours move, or where they sit outside a single daytime span. It is a description of the rota. It is not, by itself, a rate of pay or a special legal category with its own wage.
What people mean by it
A daytime job that always runs nine to five is not usually called shift work. A breakfast open, an afternoon, a close and an overnight are. So is a week that rotates, so that the person who opened this Monday closes next Monday. The useful test is whether the plan has more than one shape of day, or whether the day itself crosses into the evening or the night. The name does not change the contract. The times on the published rota do.
In Shiftbrook each of those blocks is a shift: a person or an open shift, a date, a start, an end, a place and a break. Drafts stay hidden. Staff see the week after you publish it. A rolling cycle and a fixed week are both just shifts on dates. The product does not label a person as a shift worker, because that label does not switch a feature on.
Which rules actually apply
The rules that matter are the ordinary ones, applied to the hours that were worked. Daily and weekly rest, the 20-minute break when the day is over six hours, and the 48-hour average are in the working time guide. If the shift regularly includes at least three hours in the night period, the night-work rules can apply as well. Holiday for a regular pattern is still 5.6 weeks of their own week. Holiday pay can be affected where overtime or a shift premium is part of normal pay. None of that is created by using the words shift work.
Shift workers are one of the groups GOV.UK mentions when a rest break cannot be taken at the usual time and compensatory rest may be owed instead. That is an exception to read on the rest-break page, not a reason to skip rest as a habit. Shiftbrook can warn when a saved week misses the usual rest. The warning does not refuse the save, and it does not pay anyone.
Sources
Rotas · What is a rota · Rolling rota · Working time · Night shift allowance