What is Acorn?

Legal Definition
The acorn, or oak nut, is the nut of the oaks and their close relatives (genera Quercus and Lithocarpus, in the family Fagaceae). It usually contains a single seed (occasionally two seeds), enclosed in a tough, leathery shell, and borne in a cup-shaped cupule. Acorns are 1–6 cm long and 0.8–4 cm broad. Acorns take between 6 and 24 months (depending on the species) to mature; see List of Quercus species for details of oak classification, in which acorn morphology and phenology are important factors.
-- Wikipedia
Legal Definition
When a residential area is grouped in one of the 39 ranks. It is done by age, facilities, composition, household size, marital status, income, transportation mode, job, car ownership, and home ownership. This is just a short list of possible other factors