Transverse course
A transverse course brings together students from several classes, programs or cohorts around the same course — common core, minors, cross-program electives, cross-cohort lectures.
In Omniscol, it is most often modeled with a group of groups (other software calls this a "regrouping"): you aggregate the groups concerned into a single entity, on which you place the course. It then appears in all the parent classes and remains editable afterwards — you add or remove a group without touching the structure. This is the preferred option, especially in higher education and in calendar mode.
For a one-off need, without creating a named entity, you can also assign several groups directly to the lesson from its group selector. Faster, but less readable and less reusable.
When the classes are parallel and identical in structure (same hour volumes), especially in a weekly or cyclic timetable, the alignment remains relevant: a single course shared between the groups, same time slot, same teacher, same classroom — at the cost of a frozen composition.