One-Shot
A one-shot is a comic story told complete in a single issue or chapter, not part of an ongoing series.
In depth
In American comics a one-shot is a single issue that stands alone — a special, an anniversary story, a character spotlight, or a tie-in to a larger event. It has a beginning, middle and end within its pages.
In manga
Japanese magazines publish one-shots (yomikiri, "read to the end") constantly. New creators use them to try out characters and ideas, and magazines use reader surveys to decide which deserve a full serialization. Several famous series exist as a one-shot first and a long series second, and creators' early one-shots are often collected in short-story volumes.
On the shelf
Because they are short, one-shots usually reach bookshops inside anthologies or a creator's short-story collection rather than on their own.
One-shots in American comics
American publishers use one-shots for anniversary specials, holiday issues, stories set between arcs and introductions to new characters. Collected editions often include relevant one-shots alongside the series issues, listed in the contents.
Short-story collections
For manga creators, collections of one-shots show their range across genres and periods, and often include the pilot chapter that led to their famous series. They are a good introduction to a creator's style without the commitment of a long series.
What it means today
A collection of a manga creator's one-shots is a good way to sample their range before committing to a long series.