A number whose value is defined as being anything other than itself. Found in Life, the Universe and Everything, by Douglas Adams, in the following context: Bistromathics, the study of the behavior of numbers on a waiter's check pad, frequently runs up against recipversexclusons. The most frequent is the number of people in a reservation for a restaurant, when applied to the number of people who will actually show up. Note that the behavior of numbers on waiters' check pads bears no relation to the behavior of numbers anywhere else in the Universe.