There is no part of a film's marketing that's more important than its trailer. An entire film's financial success—and a studio's very future—can be determined by a mere two-and-a-half minute preview released months in advance of a movie's premiere. Case in point: More than 13 million people watched Warner Bros.' first Wonder Woman trailer on YouTube within 48 hours of its release—giving the movie the type of buzz that executives can only dream of.

But amid all the hype attached to trailers, there's one big question that we don't really think about: Why are these previews even called trailers when they're shown before films? Well that's just the thing, they weren't always played before movies—and the very first trailer on record wasn't even for a film. It was actually for a 1913 play called The Pleasure Seekers.

As pointed out in the above video by FilmmakerIQ, the moviegoing experience was much different in 1913. You would pay your admission—usually just a couple of cents—and you could basically sit inside a movie house all day and watch whatever was playing, often a combination of feature-length movies, short films, and cartoons. To take advantage of the audience members sitting and waiting for the next movie to play, Broadway producer—and movie theater advertising manager—Nils Granlund came up with the profitable idea of advertising upcoming plays in between screening rotations at Marcus Loew's East Coast theater chain. By using rehearsal footage from The Pleasure Seekers, Granlund put together a short promotional film for the play, creating buzz and bolstering publicity for the production. He also, unknowingly, revolutionized film marketing.

In the spirit of cramming advertising into every nook and cranny of our lives, the idea quickly evolved. That same year, producer William Selig brought the popular serial format from the newspapers to the big screen—producing short action-adventure story installments that always ended with some type of thrilling cliffhanger that implored people to come back next week to find out if the hero escaped certain death. Well, how else do you get an audience back for more? Selig figured the best way to do this was to have a brief teaser for the following episode play after the main feature, so the audience would leave the theater wanting more. This was the first step toward a traditional movie trailer.

These initial trailers for Selig's first serial, The Adventures of Kathlyn, were usually nothing more than a brief bit of footage accompanied by text that screamed questions at the audience, like "Does she escape the lion's pit? See next week's thrilling chapter!" This idea worked so well that studios were soon cutting their own trailers, as opposed to the individual theaters doing it for them. After that, trailer production was outsourced by studios to the National Screen Service, which held onto a trailer monopoly for more than four decades.

Trailers soon became big business, eventually moving to the familiar position we know today, before a movie begins. This ensures more eyes on the product, and probably made more sense once the serial storytelling model was phased out. So while the term "trailer" might not make sense anymore—especially since these previews are mainly viewed on YouTube nowadays anyway—we're too set in our ways to change it now.