It is a shortened "familiar" form of the full formal form of the name. Some other examples are:
Walt's first name, Walter, came from his father, Elias Disney, who made an agreement with a friend to name their children after one another, Elias kept his end of the bargain and named his son Walter. Walt's middle name, Elias comes from his father's first name. The last name Disney comes from the Norweign name De Isigney which is believed to be converted to 'Disney' when Walt's ancestors moved to America.
December 5, 1901 Walter Elias ("Walt Disney") is born at 1249 Tripp Avenue, in Chicago, Illinois, to parents Elias and Flora Disney. Walter is named after Reverend Walter Parr.
Walter Disney
Walt Disney's full name is Walter Elias Disney!
Walter Parazaider goes by Walt.
Walter Carrasco goes by Walt.
The name of the attraction is the Walt Disney World Railroad. There are four trains that run the track, depending on the traffic on a particular day: *"Walter E. Disney," named after Walt himself *" Lilly Belle," named after Walt Disney's wife *"Roger E. Broggie," who was in charge of getting the trains *"Roy O. Disney," named after Walt's brother and business partner
Walt is a nickname for Walter Elias Disney. or it can mean we are learning to.
Walter Hyatt went by Uncle Walt.
Walter Lantz went by The Other Walt.
Walt Robbins's birth name is Robbins, Walter.
Walt Dropo's birth name is Walter Dropo.