Colony drop
A colony drop is a kinetic weapon of mass destruction. Strictly speaking, a colony drop does not need to specifically involve a colony; any structure over 1 kilometer on its longest dimension (some Zentradi ships, mining asteroids, asteroid bases, etc.) can be used to perform a colony drop.
During a colony drop, the mass is accelerated into another mass (Earth, the Moon, another colony or asteroid base) with an eye toward having it land on a specific target. Small deflections in space can lead to significant changes in target.
Defense against a colony drop usually requires stopping the mass in space, either with one's own large mass or with mobile weapons. Once a colony breaches the atmosphere, it can still be slowed to allow additional time for evacuation, but damage is essentially guaranteed.