what is the historical account behind this?
The term was coined in the US in the early 1970s; with the proliferation of the format in the 1980s and 90s, television films broadcast over even two or three nights were commonly referred to as miniseries
History
Before the term was coined in the US in the early 1970s, the ongoing episodic form was always called a "serial", just as a novel appearing in episodes in successive editions of magazines or newspapers is called a serial. In Britain, miniseries are often still referred to as serials.

Several commentators have offered more precise definitions of the term. In "Halliwell's Television Companion", Leslie Halliwell and Philip Purser argue that miniseries tend to "appear in four to six episodes of various lengths", while Stuart Cunningham in "Textual Innovation in the Australian Historical Mini-series" defines a miniseries as, "a limited run program of more than two and less than the 13-part season or half season block associated with serial or series programming." Still, with the proliferation of the format in the 1980s and 90s, television films broadcast over even two or three nights were commonly referred to as miniseries.
when does marvel's the defenders take place August 18, 2017 what is the defenders? American streaming television miniseries who wrote this? Petrie and Ramirez who are the characters in this series? Daredevil, Jessica Jones, Luke Cage, and Iron Fist how did its development take place? Development began in late 2013, with Cox the first actor cast in May 2014 where is the second mentioned actress from? UNANSWERABLE how was her early days like? UNANSWERABLE what is the definition of the type of series mentioned earlier? It is a television program that tells a story in a predetermined, limited number of episodes where did it first begin? The term was coined in the US in the early 1970s
A miniseries is distinguished from an ongoing television series; the latter does not usually have a predetermined number of episodes and may continue for several years. The format in the 1980s and 90s, television films broadcast over even two or three nights were commonly referred to as miniseries. UNANSWERABLE
Miniseries Miniseries
History History
A miniseries is distinguished from an ongoing television series; the latter does not usually have a predetermined number of episodes and may continue for several years.   the format in the 1980s and 90s, television films broadcast over even two or three nights were commonly referred to as miniseries.
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Miniseries [SEP] History
A miniseries is distinguished from an ongoing television series; the latter does not usually have a predetermined number of episodes and may continue for several years. Before the term was coined in the US in the early 1970s, the ongoing episodic form was always called a "serial", just as a novel appearing in episodes in successive editions of magazines or newspapers is called a serial. In Britain, miniseries are often still referred to as serials. Several commentators have offered more precise definitions of the term. In "Halliwell's Television Companion", Leslie Halliwell and Philip Purser argue that miniseries tend to "appear in four to six episodes of various lengths", while Stuart Cunningham in "Textual Innovation in the Australian Historical Mini-series" defines a miniseries as, "a limited run program of more than two and less than the 13-part season or half season block associated with serial or series programming." Still, with the proliferation of the format in the 1980s and 90s, television films broadcast over even two or three nights were commonly referred to as miniseries.