The term "serial" refers to the intrinsic property of a series — namely, its order. In literature, the term is used as a noun to refer to a format (within a genre) by which a story is told in contiguous (typically chronological) installments in sequential issues of a single periodical publication.
More generally, "serial" is applied in library and information science to materials "in any medium issued under the same title in a succession of discrete parts, usually numbered (or dated) and appearing at regular or irregular intervals with no predetermined conclusion."1
In the 19th century, many writers earned a living by writing stories in serial form for popular magazines.
Many of Charles Dickens' novels, for example, were originally published in this manner, and that is the reason that many are so long — the more chapters Dickens wrote, the longer the serial continued in the magazine and the more money he was paid.
Online serials have been used to create fictional communities, as in Presence, or to reinterpret and comment on actually existing communities, as in Sydney Shards.
^ Waisman, Sergio (2003), "The Thousand and One Nights in Argentina: Translation, Narrative, and Politics in Borges, Puig, and Piglia", Comparative Literature Studies40 (4): 351-71