Cottage Industry

The industrial production of lumpy cheese. Also, a term given to niche markets.

Technically, a cottage industry refers to a business done out of the home. Like...you cobble shoes in the back room of your cottage (until nighttime, when you contract out to a bunch of elves).

Historically, the term originates from this type of production. We're talking back in the black-soot London of Dickens. Companies would contract skilled workers to make small batches out of their homes. Before the rise of the big factories in the early industrial revolution, a lot of manufacturing got done this way.

Now, this literal definition has some currency again, as a sizable number of people earn money through crafts they make in their homes (think: Etsy).

But there's a more metaphorical connotation that comes up a lot too. A cottage industry can refer to a narrow market that has gained some popularity. As in, "lambasting DC's superhero movies has become something of a cottage industry among critics."