(1) An interval which includes its end values. E.g. an interval from 0 to 10, which includes the values 0 and 10 within itself. A closed interval is denoted with square brackets; [0, 10]. By default, all intervals are treated as closed in Rhinoceros and Grasshopper.

(2) A curve with coincident start and end points.

(3) A surface in which every edge is adjacent to two faces.