Dueling Pianos is somewhat of an ambiguous term. For those who have never heard of it, they often imagine two piano players competing with each other. Historically, this is correct. The late 19th century may have given birth to that concept, as ragtime pianists did compete with each other to see who could play better and faster.
In 1933, New Orleans opened what would later become (perhaps) the first dueling piano bar which is common to the standards of today’s dueling pianos. These days, customers often write their favorite songs on cocktail napkins, and bring them up to two pianists at two pianos (head to head,) who play and sing all requests.