noun /ˈo.tɚ/
In recent years the western or horse opera, known in the trade as the "oater," has come to be recognized as an art form just as formal as the ballet or the symphony. In essence it is the American morality play. To prove his contention that all this is so, Life Photographer John Florea took these unusual pictures during the filming of Yellow Sky. This is a $1,450,000 western with big-name stars (Gregory Peck, Anne Bancroft, Richard Widmark) and technical talent from 20th Centurys top drawer, but is basically a typical oater.
Wikipedia foundation.