Mid-continuum (median), as I understand and experience it*, is a condition where an individual has a natural inclination towards being able to "divide" his or her consciousness within the body into a potentially infinite number of alternate personalities, splinter personalities, and temporary or permanent mental constructs without being lessened. It is our belief that, since the minds of mid-continua (medians) mirrors the nature of the soul, that this means that medians/mids are born with their mind being very close to their soul (though we suppose it could be possible for someone to become this way after birth, even though we haven't seen it yet.)
To explain mid-continuum in more detail, it is like the ancient Egyptian Gods. In ancient Egypt, gods like Amun and Ra - normally separate entities - could be combined into entities like Amun-Ra. It is much the same way for me, as a mid-continuum. I can coalesce my consciousness into new system-mates if I choose to, or re-absorb system-mates back to the whole. Because I believe in democracy, of course, I let the existing ones choose when to be re-absorbed and when to return (re-absorption or re-integration, in my system at least, is not usually permanent).
Because of the nature of my system, everyday life is a constant flux of system-mates coming, going, and hiding out. Most of the time, the current members of my system are all awake and, thus, influencing me to some degree (I, Tristan, am called the Omni-Personality, meaning I speak for the group. I'm like an Overmind.). This means that any of my system-mates could front at any time. It also means that thoughts, memories, words spoken, or deeds done can be difficult to pinpoint the source of. They all, of course, come from "me," but the question is always, "which me?" Though some behaviors are easier to pinpoint than others... for example, Alexander Antonin is usually the grumpy one, and Molly Elizabeth is usually the one from whom childish behaviors arise. But of course, there are combinations of system mates, like Molly-Alexander (young Alexander), Molly-Lo (young Lolita Leigh Smith), Fayanora-Alexander, Tristan-Fayanora (the most common combination), and so on. (Though, due to my nature, these merely point out the strongest influences to the group at a given time.)
Lately we have been doing a lot of experimentation with individuations... each of us has been becoming more individual.
Hope that explains it. :-)
Update: Even though I intellectually understood and accepted what this meant about my nature, I had problems emotionally accepting it. I knew I was not a true multiple, but I was acting like I was, trying to individuate the others too much. In fact, just thinking of them as other people in my head rather than other forms of myself was causing problems. Psychological problems I had not had before cropped up, like panic attacks, paranoia, fear of strangers, and even fear of the dark. Once I realized the problem and began thinking of them as other forms of myself, as names for myself when my mind shifted into a particular "shape," the problems went away. I still interact with them as though they were "others," and so the positive benefits remain, but keeping constantly in my mind the awareness that they are just labels for different Aspects of my self keeps me grounded and whole and stable.
Q. How does this "mimic the nature of the soul"?
A. In our studies, we have found that most of the world's major religions either believe or teach in their scriptures the theory that souls are like God... infinitely powerful, yet capable of artificially limiting themselves in order to experience mortal life. Furthermore, it seems to us that the part of a person called the Ego - the mind and identity of the person - is just one part of the soul, as is the body. Body and mind are born from forgetfulness... forgetfulness about this reality being a virtual reality game for the soul.
The soul being infinite, as well as the mortal world and Time being illusions made for the sake of the game of life the souls play, the soul itself experiences all of its multitude of incarnations at one time (from its perspective) and yet, at the same time, experiences life from our mortal perspective. Thus, this makes the soul - in a sense - a Multiple. Or, more accurately, a mid-continuum. (God is also much the same way.)
Q. What are some of these terms, like "fronting," and "system"?
A. Here is an excellent glossary of "multiplicity" terms.
* I can only speak for myself in this matter.