Red band trailer
A red band trailer is a theatrical trailer intended to be shown to mature audiences only. It often includes images and dialogue deemed too raunchy or violent for the green band trailer, which it may otherwise resemble.
Red band trailers were often sent to theaters with the proviso that they could only be shown before certain R- and NC-17-rated features. In the analog realm, nothing technically prevented a projectionist from screening a red band trailer before any feature, other than a conscience and the potential ire of patrons.
As red band trailers are generally rarer than green band trailers, they are prized by film collectors.