Euler diagram

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A diagram representing some sets by contours of closed shapes, typically circles and ellipses, and indicating the relationships between the sets: (1) by overlapping the shapes to show that the corresponding sets have a non-empty intersection, (2) by enclosing one shape entirely within another to show that the former set is a subset of the latter, and/or (3) by showing completely separate shapes to show that neither of these two aforementioned facts applies to the corresponding sets. Also — and unlike for Venn diagrams — there is no restriction on the total number of connected regions (whether simple or not) into which the space of the diagram gets split into by the criss-crossing contours.