In order for an improvised scene to be successful, the improvisers involved must work together responsively to define the parameters and action of the scene, in a process of co-creation. With each spoken word or action in the scene, an improviser makes an offer, meaning that he or she defines some element of the reality of the scene. This might include giving another character a name, identifying a relationship, location, or using mime to define the physical environment. These activities are also known as endowment. It is the responsibility of the other improvisers to accept the offers that their fellow performers make; to not do so is known as blocking, negation, or denial, which usually prevents the scene from developing. Some performers may deliberately block (or otherwise break out of character) for comedic effect—this is known as gagging—but this generally prevents the scene from advancing and is frowned upon by many improvisers. Accepting an offer is usually accompanied by adding a new offer, often building on the earlier one; this is a process improvisers refer to as "Yes, and..." and is considered the cornerstone of improvisational technique. Every new piece of information added helps the improvisers to refine their characters and progress the action of the scene.
Improvisational Theatre Wikipedia