Short for
improvisation.
Improv, as a technique found in the performing arts (theatre, music, and dance) is based on the artists' willingness to create spontaneously, to be open to the process of spontaneous creation, and the trust that one's partners in collaboration believe in the same. Improv is used as both a training approach and as a performance form.
Key differences in the technique applied to these art forms: improv music and dance may jettison all preconceived vocabularies entirely, trusting that what is created in the moment is valid. Improv theatre is a narrative art form-- whether or not language is involved, the artists are working towards creating a story. As such, improv theatre relies on an underlying structure that improv music (and here I refer to free improvisation, not the more traditional playing changes of jazz) and improv dance do not require.