L. Frank Baum's most famous book still holds a mystery: How did the journalist, actor, axle-grease salesman, and prolific author come up with the name 'Oz' for 'The Wizard of Oz'? Various explanations have been offered by Baum's biographers. Take your pick: (1) It's a variation on the land of Uz, Job's homeland. (2) It is echoic of the 'oohs' and 'aahs' of his children. (3) It's a variation of 'Boz,' pen name of Charles Dickens, who was Baum's literary hero. (4) He derived it from the heading on a filing cabinet labeled 'O-Z.' (5) The book is an elaborate allegory about the gold standard, a hot topic at the time the book was published in 1900, and 'Oz' is from the abbreviation for 'ounce,' as in 'ounces of gold.'
Source: 'The Uncyclopedia: Everything You Never Knew You Wanted to Know,' by Gideon Haigh (Hyperion, 2004).