[Adta] defining improvisation

[Luv Seamon]

I was in a meeting at work this morning with my clinical team of art,
music, drama, and dance therapists, and we were reviewing an article
about a particular treatment model that stresses the importance of
improvisation in both the creative and therapeutic process (The Creative
Axis).  In our discussion we discovered that we all had very different
views on what actually defined improvisation (somewhat informed by our
different artforms).  I have taken on/been given the task of trying to
compile a "comprehensive" definition of improvisation and was wondering
how others defined improvisation for themselves.  I'ts not something
i've really ever thought about defining before, particularly because it
encompases so many things.    
so 
what is your definition of improvisation?

I am compiling all of the responses to this question that I receive, and
would be happy to share them with others as well.
thanks
Luv Seamon