An Expectation

1. The act or state of expecting or looking forward to an event as about to happen.
2. That which is expected or looked for.
3. The prospect of the future; grounds upon which something excellent is expected to occur; prospect of anything good to come, especially of property or rank.
4. The value of any chance (as the prospect of prize or property) which depends upon some contingent event.
5. (statistics) The first moment; the long-run average value of a variable over many independent repetitions of an experiment.
6. (colloquial statistics) The arithmetic mean.
7. (medicine, rare) The leaving of a disease principally to the efforts of nature to effect a cure.

(value of any chance): Expectations are computed for or against the occurrence of the event.

(colloquial statistics, arithmetic mean): arithmetic mean; average