Here are a few terms taken from the “Glossary of Terms” of my book, Your Strength to Heal :

Codependency
Codependency is a learned behavior that can be passed down from one generation to another and an overinvolvement in how other people feel, to the codependent's detriment. It is an emotional and behavioral condition that affects an individual's ability to have a healthy, mutually satisfying relationship. It is also known as “relationship addiction” because people with co-dependency often form or maintain relationships that are one-sided, emotionally destructive and/or abusive. The disorder was first identified about ten years ago as the result of years of studying interpersonal relationships in families of alcoholics. Codependent behavior is learned by watching and imitating other family members who display this type of behavior.

Dissociative Identity Disorder
When faced with overwhelmingly traumatic situations from which there is no physical escape, a patient may resort to "going away" in his or her head. This ability may be used and is extremely effective defense against acute physical and emotional pain, or anxious anticipation of that pain. By this dissociative process, thoughts, feelings, memories, and perceptions of the traumatic experiences can be separated off psychologically, allowing the patient to function as if the trauma had not occurred.

Often, even after the traumatic circumstances are long past, the leftover pattern of defensive dissociation remains. Chronic defensive dissociation may lead to serious dysfunction in work, social, and daily activities. Repeated dissociation may result in a series of separate entities, or mental states, which may eventually take on identities of their own. These entities may become the internal "personality states." Changing between these states of consciousness is described as "switching”.

Eye Movement Desensitization and Reprocessing
EMDR is a psychotherapy approach that helps a person to complete the “stuck” or incomplete processing of upsetting experiences, including abuse and other trauma. It includes certain distinctive features, such as the use of eye movements or various other forms of bilateral stimulation (BLS) to facilitate the person's own innate healing processes. However it is important to understand that EMDR is a complete therapy approach with several different phases.

Flashbacks
A type of spontaneous abreaction common to victims of acute trauma. Also known as "intrusive recall," flashbacks have been categorized into four types:

• dreams or nightmares
• dreams from which the dreamer awakens but remains under the influence of the dream content and has difficulty making contact with reality
• conscious flashbacks, in which the person may or may not lose contact with reality and which may be accompanied by multimodal hallucinations
• unconscious flashbacks, in which a person "relives" a traumatic event with no awareness at the time or later of the connection between the flashback and the past trauma.

Putnam Frank W. (1989). Diagnosis and Treatment of Multiple Personality Disorder . New York: Guildford Press

Integration
Integration is used to describe two different processes. One is the processing and acceptance of the trauma – an integration of experiences. The other sense of the word is the actual merging (or fusion) of two or more alters to become one. Nothing is lost: all memories, talents, and personality traits are preserved, but organized in a different way. One survivor described integration as “falling in love with myself” rather than as the death of part of herself, as she had feared.

Some people do not fuse and find that their lives are perfectly satisfactory as long as their alters are communicating well. Others fuse partially, reducing the number of alters. Most people with many alters do this in stages, allowing for time for the system to stabilize and get used to the new internal organization. Some people “become one” for a period of time and then either new alters are formed to deal with new life circumstances or the former alters split off and become themselves again.

Living with being multiple is an on-going process, just like living with not being multiple is. There are choices to be made, decisions that make life easier or harder. There is no hard and fast rule about what the “best” way is - each person's path in life is unique
( http://www.ra-info.org/faqs/ra_faq.shtml#integration ).

Internal System
A descriptive term for all the aspects or parts of the mind in an individual with DID (MPD). This includes personality states, memories, feelings, ego states, entities, and any other way of describing dissociated aspects of an individual. Understanding the parts as a system rather than as separate personality states provides an important frame of reference for treatment. Also called internal system or personality system.

M.P.D.
Multiple Personality Disorder, which is now called Dissociative Identity Disorder (see definition for D.I.D.).

Multiple/Multiplicity
In some children, the mental fragments are organized or arranged into “personalities” which seem to have a history and a life of their own. Often the personalities are so separated that they are not aware of each other's existence. This is called an amnesic barrier.

Imagine a child with a mother who is loving one moment and cruel and sadistic the next. The child will obviously react differently, depending on the mother's mood. The child will learn different ways of responding to the “good” mother and the “bad” mother. All children do this to some extent because no adult is perfectly consistent.

Now imagine that the child is so stressed out that memories of interactions with the “bad” mother are dissociated. When the “good” mother is around, the child has no knowledge of the “bad” mother, or of the “bad” child. But as soon as the mother turns nasty, the child switches, and knows exactly how to react ( http://www.ra-info.org/faqs/ra_faq.shtml#multiplicity ).

P.T.S.D.
Post-traumatic stress disorder (PTSD) is an anxiety disorder that can develop after exposure to a terrifying event or ordeal in which grave physical harm occurred or was threatened. Traumatic events that may trigger PTSD include violent personal assaults, natural or human-caused disasters, accidents, or military combat.

Many people with PTSD repeatedly re-experience the ordeal in the form of flashback episodes, memories, nightmares, or frightening thoughts, especially when they are exposed to events or objects reminiscent of the trauma. Anniversaries of the event can also trigger symptoms. People with PTSD also experience emotional numbness and sleep disturbances, depression , anxiety , and irritability or outbursts of anger. Feelings of intense guilt are also common. Most people with PTSD try to avoid any reminders or thoughts of the ordeal. PTSD is diagnosed when symptoms last more than 6 months.

Physical symptoms such as headaches, gastrointestinal distress, immune system problems, dizziness, chest pain, or discomfort in other parts of the body are common in people with PTSD. Often, doctors treat these symptoms without being aware that they stem from an anxiety disorder
(http://www.ncptsd.va.gov).

Trauma
Traumatic experiences shake the foundations of our beliefs about safety and shatter our assumptions of trust.

Trauma symptoms are probably adaptive and originally evolved to help us recognize and avoid other dangerous situations quickly—before it was too late. Sometimes these symptoms resolve within a few days or weeks of a disturbing experience: not everyone who experiences a traumatic event will develop PTSD. It is when many symptoms persist for weeks or months, or when they are extreme, that professional help may be indicated. On the other hand, if symptoms persist for several months without treatment, then avoidance can become the best available method to cope with the trauma—and this strategy interferes with seeking professional help. Postponing needed intervention for a year or more, and allowing avoidance defenses to develop, could make this work much more difficult.

We create meaning out of the context in which events occur. Consequently, there is always a strong subjective component in people's responses to traumatic events. This can be seen most clearly in disasters, where a broad cross-section of the population is exposed to objectively the same traumatic experience. Some of the individual differences in susceptibility to PTSD following trauma probably stem from temperament, others from prior history and its effect on this subjectivity.

In the "purest" sense, trauma involves exposure to a life-threatening experience. This fits with its phylogenetic roots in life-or-death issues of survival, and with the involvement of older brain structures (e.g., reptilian or limbic system) in responses to stress and terror. Yet, many individuals exposed to violations by people or institutions they must depend on or trust also show PTSD-like symptoms—even if their abuse was not directly life-threatening. Although the mechanisms of this connection to traumatic symptoms are not well understood, it appears that betrayal by someone on whom you depend for survival (as a child on a parent) may produce consequences similar to those from more obviously life-threatening traumas. Examples include some physically or sexually abused children as well as Vietnam veterans, but monkeys also show a sense of fairness, so our sensitivity to betrayal may not be limited to humans. Experience of betrayal trauma may increase the likelihood of psychogenic amnesia, as compared to fear-based trauma. Forgetting may help maintain necessary attachments (e.g., during childhood), improving chances for survival; if so, this has far-reaching theoretical implications for psychological research. Of course, some traumas include elements of betrayal and fear; perhaps all involve feelings of helplessness
( http://www.trauma-pages.com/trauma.php ), David Baldwin's trauma pages.

Triggers
Triggers are situations, actions, or words that bring a memory or feeling to consciousness or that activate a program. They are catalysts, so to speak. Some common devices used to activate programs are telephone calls, letters or greeting cards, and meaning-laden objects sent as “gifts.”

The word trigger is used in a very broad sense and may mean anything from following a command after seeing a hand signal to having a flashback at the dentist to getting upset when a friend, co-worker, or supervisor is rude or thoughtless. For clarity, it is a good idea to always specific exactly what was triggered, e.g., program, action, emotion, memory, etc.
( http://www.ra-info.org/faqs/ra_faq.shtml#cues ).