"Ehon" means "picture book," that is, a volume comprising pictures along with some text, or the text of a book with some illustrations. Hokusai's "One Hundred Views of Mt. Fuji" is a picture book composed mainly of prints, but so is the first printed edition of the "Tales of Ise," which has some illustrations amid the text.
The idea of the two arts (writing and drawing) coming together is not unique to Japan, but it probably has a longer history here. The first Japanese printed book, a Buddhist text, was published in the 8th century, and though it had no pictures, it was printed in an edition of 1 million copies. Later editions had illustrations.
One of the outcomes of Japan's early combination of text and pictures was the idea that a new experience was being created by two artists working together. The poet Akera Kanko once set out with a group of friends to collect shells along the Shinagawa beach. Everyone then wrote poems about what was found. When the text was to be published (1789), it was decided that illustrations were needed and Kitagawa Utamaro was commissioned to create these. The result is a very beautiful ehon with both text and picture on the same page -- a famous poet and a famous artist had contrived a new experience for the reader.