Omnibus

An Omnibus (Latin for "for all") is usually several novels/issues collected in a single volume. In most cases, each installment had been published in some form, either as a standalone work, or as a part of another collection. Omnibuses are often published as a way to earn more money, or to release out-of-print installments. Another occasion is for a milestone, like the anniversary of a work or for the release of the last installment in a series. The publishing industry sometimes refers to these as "bind-ups".

Similar to the omnibus release is the manga industry's tankobon, which is a recopilatory volume that collects a couple months' worth of weekly releases of one single manga, in contrast to the weekly releases published on periodic anthologies such as Shounen Jump.

Related to Anthology. Compare Compilation Movie. Contrast Multi Volume Work.

Examples of Omnibus include:

Anime and Manga

There's an Azumanga Daioh omnibus that compiles the entire series into a single volume. It's around 700 pages long.
Viz has compiled Dragonball Z and Rurouni Kenshin into "Viz Big" editions that contain three or four volumes each. Likewise, One Piece has also received this treatment, but isn't under the Viz Big name.
Dark Horse Comics has started doing this with many manga series, including several CLAMP works.
Negima is being re-released in Omnibuses in North America with a new translation job, in order to replace the first 21 volumes which had varying levels of dubious quality.

Comic Books

Comics in the Star Wars Expanded Universe have been getting combined into books much larger than graphic novel. They're each called an "Omnibus", and contain two to three arcs, each composed of four comics. This started with the X Wing Series, which has a total of three omnibuses.
Comic books in general nowadays tend to be collected in Trade Paperback editions collecting a story arc; hence Writing for the Trade.
- Marvel and DC also put out "Essential" and "Showcase" editions of older comics: phone book-sized books in black and white collecting a larger series at a time, usually 20 issues or more. Plus the "absolute" editions, which are in color on high quality paper, usually with extras.
- And of course both Marvel and DC have books called Omnibuses: Hardcover books with high quality pages larger than normal comics and with huge page counts, at the cost of a hefty price tag.
The original Official Handbook of the Marvel Universe comics have been compiled into paperback books.
The first seven Danger Girl comics were reprinted in a paperback book.
Bone was initially published as individual issues, which were collected into nine trade paperbacks... which were then republished as the One Volume Edition. It's a 1300-page tome.
Elf Quest was at one point collected into a single limited-edition volume containing the original 20-part series - a mere 652 pages. (Strictly speaking a compilation of compilations, collecting 4 volumes containing 5 parts each.)
Many of the older Buffy the Vampire Slayer comics have been published in omnibus form, as have many Angel ones. Ditto the early Buffy tie-in novels.

Literature

Most of the Dragaera novels have been reprinted in omnibus editions, with two or three novels to a book.
The Vorkosigan Saga also has a number of omnibuses; all of them have "Miles" in the title after the primary series protagonist except for Cordelia's Honor, which collects the novels where Cordelia is the protagonist. Memory—the capstone novel of the series—remains in print separately despite the fact that the two novels after it have already been collected as Miles in Love.
The Sector General books have been collected into four omnibus editions of three novels each. Confusingly, the novels themselves are mostly Patchwork Stories pieced together out of shorter works.
The Big Book of Amber reprints all ten Amber novels in a single volume.
The three Lord Darcy books (Murder and Magic, Too Many Magicians and Lord Darcy Investigates) were made into one book entitled Lord Darcy.
The 12 Thieves' World books have been combined into 4 collections: Sanctuary, Cross-Currents, The Shattered Sphere and The Price of Victory.
Lloyd Alexander's five Prydain books were joined into The Prydain Chronicles.
Harper Collins has published several one volume compilations of the seven The Chronicles of Narnia books.
The "Invasion" series of Star Trek novels.
Lord Peter, a collection of Dorothy L. Sayers' short stories starring Lord Peter Wimsey published in 1986.
The Ciaphas Cain omnibusses demonstrate the kind of exaggerated propaganda Cain is used for: a commissar with bulging muscles standing triumphantly Atop a Mountain of Corpses with an unbelievably smug grin, or with a Blade Above the Shoulder and a smoking Hand Cannon. Note that Cain is tall but not particularly bulky, and prefers a smaller and more accurate laspistol to the monstrous bolt pistol he's shown with.
Dorothy Parker lives on almost entirely in various omnibus versions of her poetry and short story collections, originally created to entertain servicemen during WWII. The best known of her omnibuses are The Portable Dorothy Parker and The Collected Dorothy Parker.
Many Warhammer 40,000 and Warhammer Fantasy Battle novels series are reissued in omnibus form, each omnibus typically containing three novels. The Gotrek and Felix, Gaunt's Ghosts, Shira Calpurnia, and various Space Marine novels have received this treatment.

Video Games

Command & Conquer: The First Decade contains every game and expansion in the series up to Generals/Zero Hour, except for Sole Survivor.
Half Life 1 Anthology, a compendium of Half-Life games on the "Gold Src" engine (up to Half-Life 2, which was made in Source).