A
hobby in which only a relatively few people--only those in a certain small
sociological niche--choose to participate. Participants in these hobbies may be considered odd by those outside that particular
subculture; conversely, they might also enjoy "
freaking the mundanes" whenever they get the chance. Because of
economies of scale, niche hobbiests often have to pay more for the objects of their affection (
e.g. role-playing game books; anime videotapes) than similar items made for a broader market (
e.g. hardcover books; VHS movies).
Niche hobbies may begin as fads that reach a peak and then die back down as time goes on. The roleplaying game is an example of such a former fad; back in the early 1980s, TSR's Dungeons and Dragons (D&D) was so popular that everybody was playing it, the game earned its own (substantially Bowdlerized) Saturday morning cartoon, and it was immortalized in the opening scenes of E.T.: The Extraterrestrial. Countless copycats (such as Palladium Books'Palladium FRP) sprang up. Then, as the '80s and '90s wore on, gaming passed out of the spotlight; TSR mismanaged itself into bankruptcy and was bought by Wizards of the Coast (on the proceeds of another fad which has since faded into niche hobby, the collectible card game), which was in turn gobbled up by Hasbro.
Old gamers turned away from gaming; maturing teenagers, formerly the chief source of new blood in the marketplace, were lured away by other pursuits (such as computer games--first-person shooters or MMORPGs). The gaming market still exists, but in a relatively small niche; games that once would have sold well into the five digits now are lucky to sell a few thousand copies period (save for games such as RIFTS, which somehow still manage to appeal to a decently-sized demographic, or D&D, which appeals to the nostalgia and reputation-influenced market as well as the gamer demographic) and fans complain about the relatively high costs they have to pay to buy them--but because of the smaller market, the industry has to charge these prices simply to stay in business.
However, it is also not unheard of for a niche hobby to grow into a fad, or at least a wider area of interest. Back in the 1970s, 1980s, and early 1990s, anime, or Japanese animation, fandom was confined largely to college campuses, with few outsiders having heard or or understanding of what anime actually was. A few series, such as Speed Racer, Battle of the Planets, Voltron, Robotech, and Starblazers made it onto TV, but even so, most Americans did not realize where these shows were from, or what they had in common. A few small importing and translation studios, such as AnimEigo and A.D. Vision, began importing titles and releasing them to video, albeit expensively.
But toward the middle of the decade, this began to turn around as more and more anime fans graduated from college and went out into the "real world" where they became a large-enough demographic to attract the interests of the media. Television and cable networks started picking up anime such as Sailor Moon and Dragonball Z, and more and more was released to video and then to DVD. To this day, anime shows such as Gundam Wing and Cowboy Bebop continue to be picked up by cable companies, and movies such as Ghost in the Shell and Princess Mononoke are imported, with varying degrees of success.
(Might rescuing empty nodeshells such as this one also count as a niche hobby? :)