Technically an incunable (singular) is a book or broadsheet created with movable type set in moulds between the invention of printing by Johannes Gutenberg (See seperate entry) in 1450 and before January 1st 1501. The Latin term “incunabula” originally meant swaddling clothes – the cloth that babies were wrapped in – so the word came to refer to infancy, and by extension to the first printings of books and broadsheets. In order to equal the prestige of the expensive manuscript books which had been copied out by monks and scribes, incunabula tried to imitate hand-written books as closely as possible, often having highly ornamental initial letters for chapters.
Editors. "First Printed Books (Incunabula)". The Literary Encyclopedia. First published 10 May 2005
[http://www.litencyc.com/php/stopics.php?rec=true&UID=413, accessed 23 February 2017.]