Tuple meter may be a misspelling or a confusion between "duple" meter and "triple" meter, which refer to pieces of music with 2 beats to the bar and 3 beats to the bar respectively.
It was originally defined to be one ten-millionth of the distance from the Equator to the North Pole along the Paris Meridian. It has been slightly redefined since. ericrain: In More detail, The...