Self - publishing your work and selling a certain number of copies / making a certain amount of money. (aliventures.com)
Unless you rise to the level of a certain number of copies, publishers lose interest in your work. (lulu.com)
Before the arrival of the «agency pricing» model that Apple negotiated with ebook publishers — which allowed the publishers to decide what price Apple would charge for their books on the iPad — Amazon had deals that paid a specific wholesale price to publishers for a certain number of copies, and then it was able to charge whatever it wanted for the books in the Kindle store. (mashable.com)