Specter
A specter is the most common type of ghost found on Interlife Earth. While shades develop from violent death, apparitions from strong emotions, and ghouls from the desires of others, specters are often theorized to arise when someone dies with some unfinished business they feel strongly about—under circumstances which do not lead to their arising as one of the other types of ghosts instead. The evidence for this is somewhat inconclusive, however, and it may be that there are other factors behind a specter's divestment. Even if it does arise from unfinished business, this does not mean that once a specter finishes its business it disappears, or passes on to whatever true afterlife awaits; there has been many a recorded case of a specter finishing its unfinished business shortly after its divestment and remaining in its ghostly state for a prolonged period thereafter. (This is, in fact, often brought up by opponents of the unfinished-business theory as evidence against the theory.)
Description
More so than any other kind of ghost, specters look as they did in life, their ghostly appearance apparently based on their own self-image. Most specters look as they did shortly before their deaths, though some who think of themselves most strongly as they were in a prior period in their lives may appear as they did at that age. Unlike shades, specters are not limited to whatever outfit they died in; the self-conceptual basis of their form allows a measure of flexibility, such that specters are able to change their clothing, hairstyles, and belongings. Most specters are limited to outfits that they had actually worn shortly before their deaths, or at some time in their life that sticks in their mind; imaginative and strong-willed specters may be able to create novel looks for themselves as well. The same goes for carried items (which are inherently part of the specter and not picked up from elsewhere); most specters' belongings are chosen from a finite set of what the specter often carried in life and/or had on them at the time of death. In any case, whatever clothing the specter wears and whatever items it carries are not really separate items but a part of the specter's body, just like the accouterments of shades and apparitions—the important difference being that unlike shades and apparitions, specters can change their accouterments.
Though it's rare, a few particularly willful and perhaps semidelusional specters who picture themselves as different from how they actually were in life may resemble their self-image more than their real mortal selves. This may mean looking in better shape or more attractive than they actually were, or the reverse for specters with a poor self-image. Some obstinate or insane specters may look totally different from their mortal selves. Such strange specters are sometimes confused with apparitions, but there are significant differences between them, perhaps the most notable being, again, the specter's ability to alter its accounterments.
Abilities
While the specter's ability to vary its accouterments sets it apart from other kinds of ghost, individual specters often have other special abilities beyond that. Many relatively common specter abilities tie into the power of changing things by force of will. Specters vary widely in the breadth of changes they can make, with some only able to change between a few set outfits and others to fashion elaborate new costumes and possessions. In some cases, they can change not only their accouterments, but their own forms as well, being capable of varying degrees of transfigurement. Some specters are also able to separate accouterments from their substance, making them effectively into discrete items with no connection to themselves, without hindering their ability to form new accouterments later. This ability, known as plasmofacture, is the primary means of new objects being made in the Spirit World, and eident specters with this ability may become quite wealthy. (Indeed, it's precisely through plasmofacture that ghost money is created.)
A few specters are able to alter not only themselves and their own accouterments but other ghosts as well—perhaps permanently. Unless cognizant of some proof of the specter's benevolence, other ghosts tend to be apprehensive of specters with this power, fearing—understandably—that the specter may change them in some undesirable way. Accordingly, this power, called ghostmolding, is in some ways as much a curse as a blessing, at least from a societal point of view; specters capable of ghostmolding may become shunned outcasts. There are those who believe that ghostmolding may be much more common an ability than is generally realized, but that most of its possessors keep it a secret to avoid the ostracism it would engender.
In ghostly society
Perhaps one of the specters' greatest strengths, in the politics of the Interlife, is simply their numbers. As specters easily outnumber all other kinds of ghost—there are nearly as many specters as ghosts of all other kinds put together—, they dominate ghostly society, and tend to have an easy time putting across policies that benefit them. For this reason, many of what pass for laws in most parts of the Spirit World favor specters to the expense of other kinds of ghosts, and specters tend to be dealt with more generously in courts and other settings. There has of course been some backlash against this—and even some specters have spoken out against the injustice—but thus far the parts of the Spirit World where serious measures have been taken to reduce the pro-specter bias are few.
Nonhuman specters
While specters are the most common type of human ghost, nonhuman specters are relatively rare. This may be because beasts rarely have the sort of unfinished business that would lead to their arising as specters, assuming this theory of the specter's formation is true—though some have argued that there are actually far more nonhuman specters than should be expected if they really arose through unfinished business, and that therefore their numbers are another argument against this theory. In any case, among bestial ghosts specters are only slightly more common than wraiths, and less common than shades. Given that nonhuman ghosts rarely have any significant accouterments, or at least any they want to change (a specter of a domestic pet may be content to always keep the same wear in its interlife, as it did in life), nonhuman specters and shades aren't necessarily easy to tell apart, though they can be distinguished by the shades' improved rate of healing, among other means.