Incunabula are books which were printed, rather than inscribed, prior to the year 1500. The date is a little arbitrary, but its what most folks consider the cut off point for incunabula.
Gutenberg Bible, Volume 1, Old Testament, Exodus, Leviticus: Harry Ransom Center, University of Texas at Austin
So why does that matter today, February 23, my birthday? Because today is also the birthday of the printed book, and for us, its also the birthday of the incunabulum.
On this day in 1455, Johannes Gutenberg printed the first book in Europe using movable type: the Gutenberg Bible. Gutenberg developed his press, using movable type, in Mainz, Germany and chose a bible for his first foray into mass production. Gutenberg chose the bible because of the demand, which hand inscription kept high, due to its time consuming, and often times, inaccurate process. Gutenberg printed about 200 copies; some on vellum, and more on paper, the numbers vary according to where I've looked. Only 21 are known to still exist, that number seems pretty well established.
I should probably mention that this date, today, is the traditional date used. Most reliable sources I've read, don't mention this date. Most state that it probably took Gutenberg a number of years to complete all of his work on the bibles. In fact, on the talk pages at Wikipedia, there is an active discussion about what exactly happened on February 23rd, and how to include it in the entry on Gutenberg and his bible.
Interestingly, each of the 21 surviving copies is different. Gutenberg's work was to print the pages, and then the collected pages were folded into quires and sold. The buyer, typically churches and monasteries, would have added the illuminations and rubrications most bible users would expect to find in an inscribed manuscript copy. And then the book would be bound, according to the owner's wishes. These hand embellishments, and individual bindings, make each Gutenberg Bible unique. Compare paper and vellum copies here!
Posted wit' minutes ta spare! Happy Birthday to me and incunabula everywhere!