Circumscription

Noun

1. The act of circumscribing or the quality of being circumscribed.
2. Anything that circumscribes or a circumscribed area.<!--should this be split into 2 senses?-->
3. The definition of what does and does not belong to a given taxon, from a particular taxonomic viewpoint or taxonomic system.

   "The circumscription in the APG system of the family Malvaceae includes the former families Bombacaceae, Sterculiaceae and Tiliaceae."

4. An electoral district; used often in texts treating electoral systems in Romance countries.