Shadowcast

Shadowcast (aka Shadow Cast) is a term that emerged in the late 1980s to describe the performers and performances that grew around The Rocky Horror Picture Show.
More than standard costume copying, a Shadowcast acts along with the film when it is played in a theater with costumes and props.
In the early days of Audience Participation at Rocky Horror, people dressed up and acted along, but not for the entire film, and the props list was relegated to the smaller variety like throwing rice at the wedding scene, using water pistols to simulate rain or tossing playing cards as "cards for sorrow, cards for pain." there were wide-spread, regular casts, but not necessarily described as such. As the cult grew, casts became more and more integrated into the entire experience.
Over time, Shadowcasts began emerging at other cult films like Shock Treatment and Repo! The Genetic Opera.