also known as a pamphlet...
Some background on Chapbooks
chapbook, n -- a book of popular ballads, stories etc, formerly sold by chapmen
chapman, n, pl chapmen -- (archaic) a trader, especially itinerant
From the Old English ceapman, and connected with ceap -- barter, bargain, price, property.
So chapbooks traditionally present accessible content at a cost that won't break you.
taken from
http://www.happenstancepress.com/Chapbooks.htm