Lecture as Exposition

As a subtrope of Info Dump, an easy way to present Exposition in a story is to have a character, often a lead character, as a lecturer or teacher in a classroom, conference or boardroom.

Compare Chekhov's Classroom. Both use The Law of Conservation of Detail in a way but since Exposition is used to set up and frame the situation throughout the plot, this trope will emphasize the importance of the scene more while the Chekhov's Classroom will often be presented more as background. Also, Lectures as Exposition often tell the viewer things they need to know immediately or things they needed to know two scenes ago.

For similar tropes, see Info Dump.

Anime & Manga

 * In Mnemosyne, some Backstory about the Tajimamori and the "Fruits of Immortality" are filled in during a lecture at Mishio's high school. Notably, the lecture is on the topic of legends and myths but turns out to consist of pretty accurate truth.
 * Subverted in Neon Genesis Evangelion: it turns out the teacher's expository teaching is.
 * One entire episode of Read Or Die the TV series is devoted to a character writing the Exposition Lecture that another character has to give.

Films -- Animated

 * Milo gives two lectures on Atlantis in Atlantis the Lost Empire. The first one is actually his rehearsal for a proposal to his superiors, which he never gets to give due to them suddenly changing the time that makes it impossible for him to make the meeting.
 * How to Train Your Dragon begins with one. In the space of a 5 minute lecture, Hiccup introduces himself, the other villagers, and the different species of dragon while at the same time sounding almost like a tour guide.

Films -- Live-Action

 * Older Than They Think: This trope shows up in The Testament of Doctor Mabuse by Fritz Lang from 1933.
 * The Rite has Father Lucas explaining the basics of exorcism in lectures at the beginning of the film.
 * In Knowing, Nicholas Cage's character gives some basic information about the sun and the fate vs. free will philosophies during his college lectures.
 * A class presentation but one not from a teacher, Sam attempting to sell his stuff at Show and Tell in Transformers when told to give a lecture on his ancestors as part of his grade. However, he is distracted by Megan Fox doing that weird thing she does with her teeth.
 * In Revenge of the Fallen, Sam has a "full-blown meltdown" in the middle of the first day of astronomy class, and ends up babbling at breakneck speed about various things that become important later on in the film.
 * This is how we learn the main complication in Give My Regards to Broad Street -- in a board meeting.
 * Jean Grey at the beginning of the first X-Men movie.
 * Serenity starts out with one of these (a teacher giving a history lecture to a group of young children).
 * It isn't clear from the very beginning due to the matryoshka-doll-like Framing Devices at work, though.
 * Stargate opens up with Daniel Jackson giving a lecture on why he believes the ancient Egyptians did not build the great pyramids. The people listening to him all walk out at the ridiculousness of the theory. In a radical plot twist that surprises no one, he was right.
 * The Final opens with a High School history teacher describing how the Han Dynasty would sometimes leave their defeated enemies alive, disfiguring them in order to serve as an example to those who would oppose them. Guess what a group of pissed-off teen outcasts do with this knowledge...
 * Urban Legend tells us about, well, Urban Legends by means of a lecture given in a college classroom.
 * 21 has Kevin Spacey's professor character tell us about the Game Show Problem during a lecture. He is an MIT professor after all.

Literature

 * In Dan Brown's book The Lost Symbol, Robert Langdon lectures his symbology class on the secrets of Freemasonry.
 * Dan Brown's characters are always giving lectures that have plot relevance. He's unable to write a story without having some sort of professor character and he has to show the professor character teaching.
 * The Harry Potter series occassionally uses these (in addition to Chekhovs Classrooms). For instance, Professor Binns' (McGonagall in the movie) retelling of the Chamber of Secrets legend and Moody's demonstration of the Unforgiveable Curses.
 * In The Name of the Wind, this tends to be the way the reader learns more about the world. It's occasionally presented as a story or myth, instead.
 * The Assassins of Tamurin teaches the reader the history of the Constructed World via a session of the heroine's history class.
 * The Functional Magic of the Mistborn series, allomancy, gets explained to the readers through Kelsier's lessons to Vin.
 * In Ashes Of Victory, Honor Harrington has been assigned shore duty as a Military Academy instructor while she recuperates from (extensive) injuries she suffered in the previous two books. We are treated to a number of such lectures, including one where a junior officer mortifies a group of awe-stricken midshipmen by calling Honor's tactics in a recent operation horribly reckless, stating that she only came out alive because the enemy simply wasn't paying attention that day.

Live-Action TV

 * On Relic Hunter, Sydney was telling her class about a particular Indian tribe's mysterious shift in culture right before she went out and solved the mystery.
 * Stargate SG-1: Jack O'Neill's young clone lectures a class of pilots on the new fighter plane.
 * Also the original Stargate has as its Establishing Character Moment for Dr. Jackson a lecture he is giving to a room of experts about his theory of the pyramids being made to replicate a design of an older, more advanced civilisation.
 * Buffy did it in "Hush", where everyone's voices have been stolen. Giles delivers the exposition through transparencies and mime.
 * In Game of Thrones, Maester Luwin teaches Bran of the various Houses vying for power in Westeros, which also serves to educate the audience on the matter.

Webcomics

 * One Tales of the Questor side story was a classroom lecture about the setting's Minovsky Physics. (In the storyline, it functioned as the first step in Doing in The Wizard.)
 * Thomil of Juathuur shows us how it's done.
 * Bob and George As a flashback

Video Games

 * Tales of Symphonia introduces its Cliche Storm plot in this only moderately cliched way.
 * Gabriel Knight: Sins of the Fathers has Gabriel attending a lecture at Tulane University early in the game where he learns some important concepts and terms relating to Voodoo.