What is "off book"

a. 1 (context theater English) No longer needing the script to rehearse. 2 below the list price

Off Book is a web show on digital culture and art created for PBS by Kornhaber Brown, a Webby award-winning production studio that creates web series, videos, and motion graphics. The series has been viewed more than six million times, and is the most shared documentary series ever online. It has been featured on prominent websites including Wired, The Huffington Post, The Atlantic, Fast Company, Gizmodo, Engadget, Mashable, USA Today, and dozens of other communities across the web.