Which type of theatre focuses on improvisation and unscripted performances?

Improvisational theatre, often called improvisation or improv, is the form of theatre, often comedy, in which most or all of what is performed is unplanned or unscripted, created spontaneously by the performers. In its purest form, the dialogue, action, story, and characters are created collaboratively by the players as the improvisation unfolds in present time, without use of an already prepared, written script.

Improvisational theatre exists in performance as a range of styles of improvisational comedy as well as some non-comedic theatrical performances. It is sometimes used in film and television, both to develop characters and scripts and occasionally as part of the final product.