lYou can use a Region object to define the geometry for a section assignment, or a load, or a boundary condition, or a mesh, basically it forms a link between the geometry and the applied attribute. A Region object can be a sequence of Cell objects. In fact it can be a sequence of quite a few other objects, including Node objects, Vertex objects, Edge objects and Face objects. In our script we are assigning a Cell object to it. But si.nce it needs to be a sequence of Cell objects, not just one Cell object that we are providing, we stick the comma at the end to make it a sequence