A farm is a planet with resources being produced yet left sitting idle, usually with little or no defense. Once the quantity of resources exceeds an attacker's projected losses for attacking the planet, the planet is deemed profitable and will be considered for raiding.
If the defending player is inactive or does not regularly remove their resources, that planet will usually be subjected to regular raiding, which in this case is referred to as farming due to its connotation of the attacker regularly collecting resources from the planet.
