Usborne
Publishing Ltd. is a
United Kingdom-based
publisher of
children's books. Their
books cover a huge
variety of
topics, but the
style of the books remains fairly
consistent - hence, when somebody talks about an Usborne book, it's not hard to figure out what they mean.
The books are (generally, though there are exceptions to this. The Usborne Puzzle Adventures and Spinechillers come to mind) nonfiction, liberally illustrated. They have pretty high information density (the books are rarely very long), giving the reader a general idea of the concept being explained.
Usborne books are very popular among homeschoolers, for fairly obvious reasons. Homeschoolers (in my perception) have a certain aversion to textbooks, and Usborne books nicely sidestep this problem. They also encourage further study.
Usborne books can usually be found at education-oriented children's bookstores, (Title Wave Books is the place to go in Albuquerque for them) or you can (I think) track them down through usborne.co.uk.
They also, I believe, pander to the short attention-span of the average noder.