expected value

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

• noun A quantity expressing a typical or average value of a random variable.
• noun The sum (for discrete variables) or integral (for continuous variables) of the product of a random variable with its probability density function, over its range of values.

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

• noun probability theory Of a discrete random variable, the sum of the probability of each possible outcome of the experiment multiplied by the outcome value (or payoff).

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

• noun the sum of the values of a random variable divided by the number of values