Several comic book series are Long-Runners, and have been published (with or without hiatus periods) for decades. Although there is usually a core cast that is always or very frequently around, and Comic-Book Time tries to make it so things stay more or less always the same, a comic book series considered in its entirety is huge, and things are not always the same. To make some order in this, the fandom and the industry divide those long-runner series into smaller units: comic book runs. Those are the periods when a certain creator has been working on the series: those times usually have a clear style, a well-defined cast, and plots are more likely to be followed from month to month than when new creators take the helm.

A run may be known for a long collaboration between a writer and an artist, but unless they cease working at the same time they are considered to last while the writer is still there. Note that a writer that left a series may return to it some years later, but this is considered a new run. Usually runs do not have a "name", unless they began in a comic with a unique name that was dropped when the run ended. Fans reference them as "Author's [comic]" to distinguish them from each other, but that's usually just a Fan Nickname.

Contrasted with comic book miniseries, contained stories with a beginning and an end. A comic book run may be structured in several Story Arcs, especially if it's Writing for the Trade. Comic book runs are open-ended and may continue indefinitely, like a sitcom. A comic book run may have an ending if the author is informed beforehand about his removal and tries to close all the open plots, especially if the comic itself will be cancelled or rebooted; but it operated in open-ended mode before that and it would be safe to assume that it would have continued doing so if there were no such orders from above.

By their nature, writers are largely Writing by the Seat of Their Pants. Sure, they may have some general outlines, some endgames to gradually build towards to, but most things are written more or less on the fly. Fandom reception and Executive Meddling are big sources of interference with too well-defined plans, but the most notable one is the Crisis Crossover. Every few months, some big events takes place and several comics have to interrupt their ongoing plots to deal with it. Of course, there are some ways to mitigate that: Superman Stays Out of Gotham (the comic does not join the crisis at all), Hero of Another Story (the current adventure does not allow the hero to join the crisis), Red Skies Crossover (there's just a background reference to the crossover), etc. It is also possible to make the tie-in comic a standalone one, not interrupting the plots at the main comic book.

Many of those long-runners are really Adored by the Network, and do not limit to a single comic book with them. Several comics starring Batman or Spider-Man may be published each month, which means that runs may not always take place in similarly named comic books. In theory, this means that there are several concurrent runs about a given character at a given time; in practice, one of those comics is the de-facto "main" one that leads the way and the others are satellites to it. Comics starred by another character from within the franchise or set in an Alternate Universe have more leeway to do their own thing with less risk of contradicting the main one.