The word for the praise on a book cover started as a joke at publishers' expense. They liked it anyway.
Gelett Burgess was a Bay Area humorist best known for a scrap of nonsense verse, "The Purple Cow," published in his magazine The Lark in 1895. His book Are You a Bromide? was selling well, and he was honored at the American Booksellers' Association dinner in 1907. For the occasion he had a special jacket made for 500 presentation copies.
The jacket showed a young woman "in the act of blurbing." Her name was Miss Belinda Blurb, and her picture was reportedly lifted from a dental advertisement. The caption read: "YES, this is a 'BLURB'! All the Other Publishers commit them. Why Shouldn't We?" The copy below promised, among other things, "gush and go."
The New York Times reported the joke on May 16, 1907, under the headline "It's a 'Blurb' Now to Puff New Book." It said Burgess had coined the term and defined a blurb as a "sound like a publisher." Two days later, in Publishers' Weekly, Burgess offered a mock history: "A blurb is a check drawn on Fame, and it is seldom honored."
The word is a little older than the dinner. In 2016 the researcher Fred Shapiro pointed to "BLURB" and "BLURBING" on the jacket of the book's 1906 first edition. Etymonline also lists a 1906 use by the scholar Brander Matthews. Yet Matthews himself, writing in the New York Times in 1922, said the word was owed to Burgess.
Burgess put the word in his own joke dictionary, Burgess Unabridged, in 1914. There a blurb was "a flamboyant advertisement; an inspired testimonial," and the verb meant to flatter from interested motives. He added that circus advertisers had started the practice and book publishers had taken it up.
Nobody claims Burgess invented the thing itself. Puffery on book jackets already existed, which was the point of the joke. What he supplied was a name sounding as silly as the practice, and the publishing trade adopted it as a plain job description. The word now covers endorsements from other writers too.