Improvisation
This term has been covered by the website Wikipedia as "Improvisation"
This mediawiki site, a `wiki dictionary` about the nature and practice of free improvisation declines to duplicate the complete content of that listing. Below there is an introduction - a simple copy and paste. from Wikipedia then a link to the Wikipedia entry.
Introduction, copied from Wikipedia
Improvisation is the activity of making or doing something not planned beforehand, using whatever can be found.[1] Improvisation in the performing arts is a very spontaneous performance without specific or scripted preparation. The skills of improvisation can apply to many different faculties, across all artistic, scientific, physical, cognitive, academic, and non-academic disciplines; see Applied improvisation.
Improvisation also exists outside the arts. Improvisation in engineering is to solve a problem with the tools and materials immediately at hand. Improvised weapons are often used by guerrillas, insurgents and criminals. Contents