Red-band trailers have become increasingly popular in the last decade or so, but what exactly does the term mean? Trailers got their name because previews for upcoming films used to be attached to the end of movies, meaning they would literally trail them. This wasn't a popular practice with exhibitors seen audiences tended to just leave once a movie ended, so they were later moved to the front. Trailers have evolved over time from lengthy, spoiler-filled previews filled with text and voice-overs to their modern form, where action-packed previews for blockbusters like Avengers: Infinity War have become events in themselves.
A good trailer can get audiences excited for a movie, giving a sense of the story, characters, and tone, be it action, comedy, or drama. Blockbusters trailers are often greeted with anticipation with trailers for movies like DC's Joker or Terminator: Dark Fate offering a first look at the story or action. A mediocre preview can work against a movie, however, with a recent example being the trailer for the musical Cats. Instead of selling viewers on the movie's use of CGI to turn actors into cats, it instead had the effect of making it look more like a horror movie.
Most trailers that are shown in cinemas in the U.S. come with a green-band label, meaning the MPAA have rated it acceptable for viewers of all ages. While most movies have a green-band trailer, if they're intended for a mature audience, this can limit what the preview can show. This is where red-band trailers come in, where are R-rated previews. Good examples include the red-band trailer for the Evil Dead remake, which was able to display some of the gruesome highlights found in the movie. These previews are also useful for displaying some of the raunchier gags found in R-rated comedies like Jay And Silent Bob Reboot or Little Monsters.
Red-band trailers used to be quite rare, but due to the rise of the internet, they've steadily increased. In some instances, they're able to better convey the tone of an R-rated film than a green-band trailer. In others, the bad language or gore they contain can cut through the clutter and help it reach the intended audience. Red-band previews are also intended to warn parents the content of a trailer is inappropriate for children, and they're supposed to be locked behind an age-gate. Yellow-band trailers also exist and are intended to convey a preview was meant for adult internet users. Yellow-band slates were briefly used for movies like Rob Zombie's Halloween but quickly fell out of use.
TV shows like The Boys and Gotham have also used red-band trailers for promotion. While they were once seen as something of a promotional gimmick, the best examples can be a great way to sell the tone of a movie.