Fields
From OGame Wiki
Fields represent the space available on a planet for buildings. Every level of a building you construct uses one field. The Terraformer can be used to increase the max fields of a planet.
All home planets start at 163 fields (regardless of position) and as a general rule planets 200+ are desirable for long-term expansion when colonizing new planets.
Defense structures do not use up fields on planets or moons.
