Image from P Bourne copyright used with permission
The term space hulk is a generic one given to massive, derelict vessels, almost always once-sentient or robot ships who's ai had failed, transcended, died, or in any other way disappeared from or been eliminated from the vessel. Although there are many smaller dead ships, it is usually the size of the hulk that makes it impressive. A hulk is valuable as salvage, and local operators have been known to charge exorbitant rates which the original owner must honour before e is allowed to re-claim it. In some cases, especially if it has been drifting for centuries or millennia, the parent or owner corporation, sophont, or transapient is no longer in existence. Because of material mass, archival data, and generic historic or heritage value, hulks are highly sought after. In the (rare) case of a transcend which left relics, they may be almost priceless.
In some instances, such "orphan" hulks are legally the property of the polity in whose space they have ended up, and the salvage operator only receives a modest (in proportion to the hulk's value) but still extremely lucrative, commission. But in deep interstellar space, or in areas where borders are vague or ill-defined, there is no clear ownership, and salvagers, prospectors, scavengers, privateers, and small corporations will usually all make attempts at claiming the hulk. It is not unknown for lives to be lost in firefights over salvage rights to owned hulks, let alone orphans.
Although hulks may bring their discoverer great riches, they can also be dangerous in and of themselves. Sometimes, even when there is no pilot ai left, the self-maintaining security systems are still functional, and these may not hesitate to use deadly force on the presumed "bandit" or "pirate" who is trying to board the vessel. For this reason, no sane salvager will board a strange hulk without sending in remotes or probes to scout and check for defenses. Clever (turingrade or higher) defense ais know to ignore the remotes and await the salvager emself.
Rarely, in the case of a transcended ai, there is a sentient trans-sapient artifact or artifacts remaining, and, although most often not intending harm, these may inadvertently subvert or dominate the unwary treasure hunters. In some rare cases these individuals, now with the relic symbiotic to them, have started religious movements, although generally these cults do not last long.
Another rare but still possible danger is that in the case of a perverted transcend, there may be a deadly and insidious trap waiting the unwary; often of a transapient-tech nature for which a sophont (or even a hyperturing) may have no defense. In rare cases, such a trap has infected and destroyed an entire polity or star system, either infecting and subverting the local Net with ai viruses, or unleashing nanolects or even attack goo, and resulting in thousands or even millions of deaths or subversions, and the necessity of quarantining an entire system. Although the number of times such a catastrophe has happened are rare (no more than 20 times in the last standard year throughout the entire known galaxy) they are sufficient to create an aura of dread and hysteria around even completely harmless and inert hulks, and countless melodramatic virches and interactives have been created along this simple plotline.
Thanks to navigation drones and distributed ai nets, hulks are usually easily detected within the inner sphere, once they approach near enough a star system. Less easy to find are hulks still drifting or moving at relativistic velocities in deep interstellar space, or further out in the periphery or around low tech and isolated systems.
The rarest of all forms of derelict spacecraft found in the Terragen Sphere are those left behind by long-vanished aliens; thess include the vessel found in the Porrima system, rare Iahi Daon ships, and the databanks left by the Archivists.
Adventurers who actively seek space derelicts for fun and profit are known as Hulkchasers; sometimes hulkchasers take up residence in derelect spacecraft far from civilisation, and become hiders known as Hulkriders.