Short answers, pulled from the story.
A fandom is a subculture of fans bound by camaraderie over a shared interest. Its members are interested in even minor details of the subject and spend significant time and energy on it, usually within a social network that sets them apart from people with only a casual interest.
Merriam-Webster's dictionary traces the term fandom back as far as 1903. It has its roots in people with an enthusiastic appreciation for sports before it broadened to apply to fans of any subject.
Feminist scholar Adrianne Wadewitz cited the Janeites, devotees of the 19th century author Jane Austen, as the earliest example of fandom subculture, beginning around 1870. Fans of Sherlock Holmes were another early example, holding public mourning after Holmes was killed off in 1893.
The furry fandom began at a science fiction convention in 1980, when a drawing of a character from Steve Gallacci's Albedo Anthropomorphics sparked discussion of anthropomorphic characters. The brony fandom emerged in late 2010 and early 2011 on the imageboard 4chan around My Little Pony: Friendship Is Magic.
Fans organized to save Star Trek in 1968, Cagney & Lacey in 1983, Xena: Warrior Princess in 1995, Roswell in 2000 and 2001, Farscape and Firefly in 2002, and Jericho in 2007. Firefly fans did not get a new season but earned the movie Serenity instead.
Early engineers traded Grateful Dead set lists and discussed the band's Wall of Sound speaker system over ARPANET, a precursor to the Internet. This led to tape trading over FTP, the Internet Archive adding Grateful Dead shows in 1995, and communities like etree evolving into peer-to-peer torrent networks.