A bounded region governed by its own conditions. A zone's edges are drawn rather than found.
Latin zona (a belt, girdle; a geographical band), from Greek ζώνη (zōnē, a belt, girdle). Greek geographers first used the belt-word for the five encircling bands of the earth — the torrid, temperate and frigid zones — before the sense loosened to name any bounded region.
A region whose edges get drawn on purpose, rather than edges the ground itself already carries. What holds inside one boundary answers to different conditions than what holds just past it.