
So before we had Interwebs to do this sort of thing more cheaply, publishers would release pocket-sized little volumes with brief essays or stories suitable for giving or carrying around in a pocket or purse. It was the equivalent of the 45 RPM single of our record days, as opposed to a LP, or full collection of stories equivalent. If all you wanted was that ONE song/article you liked, it was convenient (and less expensive.)
In the days when I used to redistribute people’s libraries, certain little hardcover booklets came in repeatedly. Some were health-related, and some were motivational tracts. But it was fiction, and frequently humor, which accounted for the perennials.
The convenience of the little booklets sometimes had side effects. Though the authors might have produced many, many more works that the one represented in the booklet, THOSE hardly ever appeared in donations. The success of their booklet eclipsed everything else the writer had done. Some of the all-time favorites in pocket reference literature include:

Ellis Parker Butler: Pigs Is Pigs: Someone ships a pair of guinea pigs to a recipient who is unable to claim them because the stationmaster at the railroad depot demands the fee charged for shipment of hogs. When the customer points out that these are GUINEA pigs, the diligent but uninformed official, Flannery, responds with the title of the poem: it doesn’t matter if the pigs are Guinea Pigs, French Pigs, or pigs of ANY nationality. Since the guinea pigs are male and female, and he is required to keep feeding the livestock and their offspring until claimed, the man grows to regret his stubbornness.
Butler produced over two dozen books and hundreds of short stories in his career. These may be all very well, but the little volume about comic Irishman Flannery’s stubborn belief went through dozens of printings. Several animated adaptations have been made, and there was even a silent movie version.

Langdon Smith, Evolution: A Fantasy: One lover expresses to another that their lives have been linked through eons of evolutionary time, beginning “When I was a tadpole and you were a fish”. Various stages in the history of their relationship are covered in the poem, concluding with a belief that whatever happens in THIS life, they will meet—and love–again.
Smith was best known as a reporter in the wild and woolly years of the late nineteenth and early twentieth centuries. His poem really burst forth in those little volumes after his death at the age of 50. His wife, in a poignant postscript to the poem, committed suicide a few months later.

Chic Sale: The Specialist: A self-trained architect reflects on his career and about the principles involved in building the structures he is famous for: outhouses. He notes the considerations which go into the proper construction of a privy: the nearness of apple trees, the efficiencies in locating an outhouse for a shy woman, especially as opposed to a more courageous one, the dangers of asking the seats so comfortable people simply want to sit and read the catalogue which is provided for purposes other than reading.
Chic Sale was a comedian who often played rural old men (HE died at 51). “The Specialist” was originally a play, but he adapted it into a monologue to be published in book form primarily to safeguard his copyright. The reception of the book meant he had to spend months answering fan mail, and led to the use of his name as a euphemism for outdoor toilets just at a time when these were starting to disappear from the scene.
There are other booklets: I might have included Corey Ford’s How to Guess Your Age or Henry Van Dyke’s The Other Wise Man, or even Clement C. Moore’s A Visit From St. Nicholas. But there’s no point making this column longer than some of the books discussed in it.