Mereology is the theory of parthood relations…

Mereology (from the Greek μερος, ‘part’) is the theory of parthood relations: of the relations of part to whole and the relations of part to part within a whole.

The term was coined in 1927 by Leśniewski, probably as a variant of the term ‘merology’ originally used to indicate the field of anatomy concerned with body fluids and elementary tissues; see Simons (1997: n. 4). In some literature, ‘mereology’ is also used with reference to work in General Systems Theory (not covered by this entry) devoted to the study of system decomposition, as in Mesarović et al. (1970). See also Winther (2011).

— Stanford Encyclopedia of Philosophy


Mereology | Stanford Encyclopedia of Philosophy

Mereology | Wikipedia
Mesarović, M. D., Macko, D. and Takahara, Y., 1970, Theory of Hierarchical, Multilevel, Systems, New York: Academic Press.
Simons, P. M., 1997, ‘Bolzano on Collections’, Grazer philosophische Studien, 53: 87–108.
Winther, R. G., 2011, ‘Part-Whole Science’, Synthese, 178: 397–427.