Handy Multiple Terms

Alter, Personality - Terms for people in a multiple system. These terms are often considered derogatory or inaccurate because they stem from an implication that there is one "real" person who has lots of "personalities." Try "person" instead.
Being Out - Both a term for not hiding the fact that you're queer/multiple, and a term meaning that someone is the person or people who are currently "out in the body" doing regular outside stuff like getting ready for bed or talking to friends.
Co-conscious - A state where two or more people are out at the same time, each aware to some extent of what the other is thinking.
DSM-IV - Stands for Diagnostic and Statistical Manual, 4th edition. It is within this manual that the diagnoses of Dissociative Identity Disorder/Multiple Personality Disorder and Gender Identity Disorder can be found.
Fronter - Someone who spends a lot of time out, taking responsibility for the body and the outside life. There are often many fronters in one system. Sometimes they are called "hosts," but that can also be a derogatory term if it's used to imply that the "host" is the only "real" or valuable person in the system.
Integration - Presented by many therapists as the "cure" for multiplicity, where the ultimate goal is to make everyone merge into one person somehow. Multiplicity has been very little understood and explored so far, partly because of the reliance of therapists on integration. This in turn means that integration often does not work, resulting in the deaths of people within a system or in a re-emergence of the supposedly integrated members. In other cases, integration just ends up meaning that everyone becomes co-conscious. It is a controversial act and issue in the multiple community. Ultimately, it can (or at least should) only be up to the people within a particular system whether to integrate or stay separate, and to figure out what that means for them.
*Losing Time - The experience of being inside while someone else was out, and missing the chunk of time that they were there. Losing time can also occur when a person in the system is out, but cannot retain memories of events.
Mid-Continuum - Mid-continuum is to multiple as genderqueer is to transgendered: completely different but totally the same and not yet fully explored even by people within its community. Also known as identityqueer.
*Switching - The act of one person in a multiple system going inside the system, while another one comes to the front.
System - A group of people sharing the same body. Many systems find a collective name for themselves, like DarkSouls or Kaleidoscope House, so that people can refer to the group more easily.
* Items marked with an asterisk are from http://www.darkpersonalities.com/terminology.htm