The cruiser is a large ship size, one step above a destroyer. By default a cruiser has a larger hold and tank than any smaller size, and a higher base structure, and it is slower.
The hauler, the deep miner, the warden and the breaker are cruisers.
Most stations are cruiser size, among them the Port, the Forward HQ and the combat station. A dock takes ships up to its station's size, so their docks take ships up to a cruiser. The hull needs no dock.