|a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.|
|a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes.|
|Heisenberg uncertainty principle, Also known as: indeterminacy principle the principle that energy and time or position and momentum of a quantum mechanical system, cannot both be accurately measured simultaneously. The product of their uncertainties is always greater than or of the order of h, where h is the Planck constant|
|uncertainty principle (ŭn-sûr'tn-tē) Pronunciation Key
A principle, especially as formulated in quantum mechanics, that greater accuracy of measurement for one observable entails less accuracy of measurement for another. For example, it is in principle impossible to measure both the momentum and the position of a particle at the same time with perfect accuracy. Any pair of observables whose operators do not commute have this property. As defined in quantum mechanics, it is also called Heisenberg's uncertainty principle. Similar uncertainty principles hold for non-quantum mechanical systems involving waves as well.