Scene painting is a technique where players describe verbally things that exist within the improvised space. Usually, you start by pointing to where the thing is, possibly miming using it or tracing its outline, saying "We see a..." or "There is a..." or somesuch variation followed by describing what the actual thing is.
Scene painting can be used as a longform opening, where improvisors paint a location or several locations. The players may either narrate as themselves or in character. The exact locations may be used for developing premises, finding patterns, or unusual things. The inspiration locations created by scene painting are often not revisited in the set exactly as they appeared, although they may.