Fandom is a term used to refer to a subculture composed of fans characterized by a feeling of empathy and camaraderie with others who share a common interest. Fans typically are interested in even minor details of the object(s) of their fandom and spend a significant portion of their time and energy involved with their interest, often as a part of a social network with particular practices (a fandom); this is what differentiates "fannish" (fandom-affiliated) fans from those with only a casual interest.
A fandom can grow around any area of human interest or activity. The subject of fan interest can be narrowly defined, focused on something like an individual celebrity, or more widely defined, encompassing entire hobbies, genres or fashions. While it is now used to apply to groups of people fascinated with any subject, the term has its roots in those with an enthusiastic appreciation for sports. Merriam-Webster's dictionary traces the usage of the term back as far as 1903. It is formed of the word fan plus the suffix (as in ).
Fandom as a term can also be used in a broad sense to refer to the interconnected social networks of individual fandoms, many of which overlap.
Fans of the literary detective Sherlock Holmes are widely considered to have comprised the first modern fandom, holding public demonstrations of mourning after Holmes was "killed off" in 1893, and creating some of the first fan fiction as early as about 1897 to 1902. Outside the scope of media, railway enthusiasts are another early fandom with its roots in the late 19th century that began to gain in popularity and increasingly organize in the first decades of the early 20th century.
A wide variety of Western modern organized fannish subcultures originated with science fiction fandom, the community of fans of the science fiction and fantasy genres. Science fiction fandom dates back to the 1930s and maintains organized clubs and associations in many cities around the world. Fans have held the annual World Science Fiction Convention since 1939, along with many other events each year, and has created its own jargon, sometimes called "fanspeak". In addition, the Society for Creative Anachronism, a medievalist re-creation group, has its roots in science fiction fandom. It was founded by members thereof; and many science fiction and fantasy authors such as Marion Zimmer Bradley, Poul Anderson, Randall Garrett, David D. Friedman and Robert Asprin have been members of the organization.