Referent
From Improvisers' Networks Online Mediawiki
Referent
Introduction
Phil Morton has come to adopt the term used referential or a referent, or he proposes those active in free improvisation acknowledge this term maybe useful
Referential simply means the improviser/musician is required to refer to an external referent, that maybe a document or idea that influences what the person does within the parameters of music.
Thus free improvisation, free ensemble improvisation should delivered without the presence of an external referent.
This is an attempt by Phil Morton to bypass the binary world of free improvisation vs composition
Source
Free Ensemble Improvisation, Harald Stenström A Thesis [1]