This is a way of designing to maximise energy efficiency. Activities are put in different zones, depending on frequency of use, maintenance, visits etc.

Generally, activities and structures are placed as follows:

Zone 0: Centre of activities - the house. This is high maintenance, high use and requires considerable investment of time and energy.
Zone 1: Annual plants, herbs, compost, plant propagation, construction and maintenance, bike store and other high use activities, greenhouse. Often irrigated
Zone 2: Dense planting, poultry and small livestock, orchard, polytunnels.
Zone 3: Large water storage, main crops, sheep, cows, field shelters.
Zone 4: Forestry, wood-pasture, dams, forage.
Zone 5: Wild zone, where nature is in charge and where we go to learn and harvest only that which is abundant.

See this article : http://permaculturenews.org/2015/12/11/permaculture-zones-of-use-a-primer/

Image Source: By Felix Müller (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons