"Because, as we are told—
a sad old joke, too—
Ghosts, like the ladies,
never speak till spoke to."
~Thomas Ingoldsby, The Ghost, 1837
You know what a ghost is, don't you? As we move closer to Halloween, we are reminded that on that night it is said that the "veil" between our world and the underworld is the thinnest, allowing ghosts to inhabit our earth as we know it, and therefore, it is the one night where the spirit world collides with the human world.
So, we must give the Devil it's Due and define a ghost.
First of all, you must make the distinction from other entities:
A ghost is not an angel, or a demon.
What you should know and is important: A ghost is always manifested as human.
According to llewelynworldwide there are 3 characteristics that must be made when defining what a ghost really is. Please note that I have edited comments, and given only the distinctions.
"The first of these—and perhaps the most important—is that ghosts are always human. To put it more precisely, a ghost is the disembodied conscious energy—that which we might call the personality—of a once living person.
The second characteristic of a true ghost is that it is interactive, at least to some degree—that is, it has the ability to manipulate matter, to observe and be observed, and have some capacity to communicate with the living... A true ghost, then, must be both human and interactive, or else it is simply something else.
Finally, the third characteristic unique to ghosts is that they are not a natural part of the spiritual realm, but beings that exist apart from it. In other words... whereas spirit guides and angels and other such denizens of the ethereal realm are a natural extension of the spirit world, ghosts are beings that are unnaturally confined to the physical realm for a variety of reasons, usually having to do with either a free-will decision to stay behind or an unwillingness to completely move on to their next level of existence.
In essence, ghosts are either “trapped” or choose to reside in a type of “twilight” state that exists between the spiritual and physical realms, effectively making them residents of neither the physical nor the spiritual realm yet subject to elements of both."