uncertainty principle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A principle in quantum mechanics holding that greater accuracy of measurement for one observable quantity entails less accuracy of measurement for another conjugate quantity.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun quantum mechanics Heisenberg uncertainty principle.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (quantum theory) the theory that it is impossible to measure both energy and time (or position and momentum) completely accurately at the same time