Infodumping is a type of Exposition that is particularly long or wordy. As Indiana Jones proves, it can be done in a way that is unintrusive or entertaining, characterize the participants, and have some wonderful music to back it all up. And there may just be situations involving Acceptable Breaks from Reality due to there being no other way to more naturally explain the plot point over the course of the story before it becomes critically important without bloating/slowing down the pacing.
Most of the time, however, infodumps are obvious, intrusive, patronizing, and sometimes downright boring because they don't advance the plot at all, especially if they have no visual aids. And if the premise of your story is laughably ridiculous, an infodump will call attention to the fact. The absolute worst is the gratuitous infodump, which painfully restates that which has already been adequately shown, just to make the audience suffer. For these reasons, 'infodump' is often used as a pejorative term. Even worse, one character may be saying it to another who is fully aware of it already (which may be called out), for no good reason besides filling in the audience. Having one character be The Watson is a common workaround to this, as their presence creates the need for other characters to exposit.
Intensive infodumping about the world itself (called Expospeak) is most commonly used in Speculative Fiction, where the reader cannot necessarily make assumptions about the way the fictional universe works. Some Speculative Fiction writers, such as Terry Pratchett and Douglas Adams, make a virtue of their infodumping (which can sometimes go on for pages) by making it funny and therefore pleasurable to read. Writers of less comedic works must work hard to avoid heavy infodumping unless they are sure that they can make it entertaining. Many choose to avoid intensive infodumping altogether through the use of supplemental material. If the character does it repeatedly, then he or she is Mr. Exposition.
In a video game, infodumps can often be in the form of a long, boring lecture from one of the characters babbling on and on, giving you pages and pages of trivial information that may or may not be useful to the player. This is a problem because video games normally involve player participation, which cannot happen in an infodump unless it's part of the level design. It's at its worst in games that only use text boxes, especially older games that can only display a few words in the box at a time. May include Shall I Repeat That?.
Specific Sub-Tropes that are always Infodumps:
