Thought I would post this, I saw it on my friend Winter's group for DID and it explains things so well
WHAT IS DISSOCIATION?
 
 Dissociation means the separation of things that were, or usually are, 
together (e.g., associated). In their minds, people usually remember a 
whole event, including sights, sounds, feelings, and meaning. When 
dissociation occurs, the remembered event may be devoid of meaning or 
feelings, which are separated and stored in another part of the mind. In
 other words, the different parts of the memory are recalled separately,
 not as a congruent whole.
 
 Strictly speaking, dissociation is a
 mental process, a way of recording and storing informa-tion. It is one 
of the mind's ways of operating. Some information may be dissociated, 
while other information is stored as a whole.
 
 Sometimes you 
hear "So-and-so is dissociated." This is shorthand for saying that their
 mind uses dissociation. A person is always a whole person regardless of
 how their mind works. Nobody stores their feet in one place, their nose
 in another, and their mind someplace else, even though some days it may
 feel that way.
 
 WHAT CAUSES DISSOCIATION?
 
 Dissociation
 occurs when a person experiences extreme stress or stimulation. Under 
these conditions, life is experienced differently, and the memory of an 
event is stored differently in the mind. Research is suggests that the 
brain operates differently when experiencing or recalling stressful and 
non-stressful events.
 
 Here is a personal example that many 
people may be able to relate to. I remember skidding badly on an icy 
street. As the car skidded, colors seemed brighter and time passed very 
slowly, I was enveloped in total silence even though the radio was on 
and I experienced no thoughts or feelings whatsoever. I was aware of 
only the visual part of this experience as it happened. Later, the 
emotions hit. I was so frightened that my heart pounded and my legs 
shook, but I could no longer call up the visual memory.
 
 When a 
child is severely abused, extreme stress occurs repeatedly. Many events 
are experienced in a state of shock, stored in a dissociative state, and
 recalled in fragments.
 
 If a child dissociates extensively, 
even memories of less stressful events can be dissociated. Perhaps the 
child is still in shock, perhaps the child's sensitivity to stress is 
raised, perhaps the mind comes to store all material in a familiar way.
 
 There are innate temperamental differences between people. Some people 
probably dissoci-ate more easily than others or require less stress to 
change over into dissociative mode.
 
 WHAT IS A FLASH-BACK?
 
 A flashback is a dissociated memory that returns to consciousness. It 
can be a smell, a taste, a sound, a picture, an emotion, or all these 
things together. It can last a moment, or linger on for weeks.
 
 
People describe smelling alcohol or perfume when none is present, 
hearing a phrase over and over again in their heads, feeling panic or 
dread for no logical reason, or seeing pictures, like snapshots or 
movies behind their eyes. All these are fragmented memories rising up 
into consciousness. They can be extremely vivid and can appear to be 
happening in the present. The more fragments come together at the same 
time, the more intense the flashback.
 
 Flashbacks are terrifying
 if you don't know what they are, and if you don't realize they will 
eventually stop. Experiencing flashbacks doesn't mean you are going 
crazy - it means that you are at a point in your life when you are able 
to deal with things that you couldn't cope with earlier. They tend to 
lose their intensity when you have assembled the fragments into a 
coherent memory, talked about it, cried about it, and absorbed the 
memory into your life.
 
 WHAT IS 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 amnesiac 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. That's multiplicity.
 
 WHAT IS AN ALTER?
 
 
An alter is one personality of a person with multiplicity. The 
personality who is "out" most of the time is often called the host 
personality, and personalities seen less frequently are called 
alternative personalities, or alters. Some people have only one or two 
alters, others have hundreds or even thousands.
 
 Some people 
with multiplicity experience each alter as a separate person. Others 
experience them as different from their usual self, but not as different
 people. Multiplicity is not exactly the same from person to person, and
 each person's experience of their inner reality is unique.
 
 
Often alters have names, have a distinct age, and have specific jobs to 
do. One may be in charge of feeling anger, another of going to school or
 work, another may be the one who decides which alter gets to be in 
control of the body at any given time. Alters may have a different 
gender from the body or a different sexual orientation from the host. 
There may even be alters who are animals, objects, or abstract ideas. 
Sometimes people have alters who are experienced as being dead or 
immortal.
 
 The formation of alters is a natural psychological 
process, given extreme early childhood stress. Abusive adults who are 
aware of the process can manipulate and train the emerging personalities
 to their own ends. Some survivors of ritual abuse have alters trained 
by their abusers to do certain tasks and to behave in ways desired by 
the abusers. And some survivors have alters organized in elaborate 
patterns designed by the perpetrators, with strict rules about how the 
alters communicate with each other.
 
 WHAT IS CO-CONSCIOUSNESS?
 
 When two or more alters are aware of what is happening in the present, 
they are said to be co-conscious. When two or more alters share control 
over the body's actions, they are said to be co-present.
 
 A 
person may have alters who are unaware of each other, alters who are 
always mutually aware of each other, and alters who are aware at some 
times but not others. Alters who are aware of the presence of other 
personalities know they are multiple, while alters who aren't in contact
 with other personalities firmly believe they are "the only one there." 
An alter may even be multiple.
 
 WHAT IS INTEGRATION?
 
 
Integration is used to describe two different processes. One is the 
process of alters learning to communicate and cooperate and sharing 
their memories with each other. 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.