PLURALITY: A state in which more than one consciousness resides within a single body, often called a system. Depending on the system, this can be a purely psychological phenomenon, one with metaphysical roots, or a mix of both, and so on.
SOULBOND (noun): A person from another world (whether that world be depicted in this world's fiction or not) who has contact with, or has appeared in, the mind of the soulbonder, through emotional, mental, or other such connections, such as astral projection, etc.
SOULBOND (verb): To create an emotional, mental, or other such connection with a person from another world, which leads to the ability to communicate with them through one's mind, or their presence within the mind itself.
SOULBONDER: A person who has made a connection with a soulbond. This does not necessarily need to be the original owner of the body.
MISCITIEN: A system defined by a tendency to constantly be flowing between multiple and median, with emphasis on a central identity that other sysmates can fuse with and stick to. More information can be found here.