information entropy

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

• noun In information theory, a mathematical measure of the degree of randomness in a set of data, with greater randomness implying higher entropy and greater predictability implying lower entropy.

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

• noun information theory A measure of the uncertainty associated with a random variable ; a measure of the average information content one is missing when one does not know the value of the random variable (usually in units such as bits); the amount of information (measured in, say, bits) contained per average instance of a character in a stream of characters.