On text improvisation is when you improvise but stay true to what is happening in the story and to your character. This is useful for building up your character emotionally because the script can often be a barrier. After using on text improvisation an actor will return to the script. The actor should find it more easy to play the character.
Spontaneous improvisation occur "off the top of the head" or without rehearsal before. Rehearsed improvisation is gone over many times and changed.
I assume you mean what that is called. The answer is improvisation, also know as improv.
There are many places in New York where you can go for improvisation classes. Some of these places include: The American Comedy Institute and the Face Off University.
Improvisation means to make it up as you go without planning it ahead of time
Solo Improvisation.
Improvisation 35 was painted in 1914.
Improvisation
Rhythmic improvisation
melodic improvisation
Prepared and spontaneous
Collective Improvisation.
Scat singing