An activity that describes a change to one or more properties of another activity, for a subset of weeks in the teaching year. For example, if for one month of the teaching year the location that is allocated to an activity is unavailable, two variants can replace the original activity in the timetable. The variant that represents the changed month is allocated a different location; the other variant's properties match the original activity except for a changed teaching week pattern. The original activity is unscheduled and hidden, and becomes the variant parent of the new activities. The variants' teaching week patterns cannot overlap.