“Lulu is an on-demand publishing tool that lets you publish and sell books, ebooks, music, images, and calendars.”

From the Knowledge Base:

“Print on demand (POD) is a method of producing books or other media (such as CDs and DVDs) one at a time.
With print on demand, a printer produces hard copies of a book from a digital file.
That way, the book is only printed when someone buys it.
With Lulu, an author gives us a digital file of the book and we create a print-ready version of the file.
When a customer buys that book from Lulu, our printer prints that copy (or copies) and ships it within days.”.