When is a piano not a piano? When it is 2 pianos of the same size put together, one on top of the other, on a special structure which has a keyboard (called a pedalboard) played by the feet, the sort of thing you see in pipe organs. It is a pedal piano and was part of the evolution of keyboard instruments.
I learned all this at a most interesting piano recital at the Royal Scottish Conservatoire. Roberto Prossedo, not... not Prosseco ... from Italy played for an hour and let us have a look at the instrument brought from Italy.
It developed in the early days of the piano as we know it today (early 1119th century) and was a welcome instrument for organists who wanted to practice. It meant that they did not have to sit in a freezing cold church and also they did need someone to work the bellows!
Photos: mine on the top and the other 2 are from Wikipedia.