Expect

Expect is a verb in English meaning to regard something as likely to happen, to anticipate, or to look forward to something. It can govern clauses with that, or be followed by an infinitive (to arrive). It can express expectation of a result, or a social obligation as in "I expect you to be on time." The noun form is expectation, referring to the anticipated outcome or the belief that something will occur. The word derives from the Latin exspectare, to look out for or await.

In probability and statistics, "expectation" or "expected value" denotes the probabilistic average of a random variable. For a discrete X with values x and probabilities p(x), E[X] = sum x p(x). For a continuous X with density f, E[X] = ∫ x f(x) dx. The expected value is a measure of central tendency used to predict long-run behavior; it satisfies linearity: E[aX + b] = aE[X] + b. It is not necessarily the most probable value (the mode). The concept extends to functions E[g(X)]. In economics and decision theory, the expected value guides choices under uncertainty.

In computing, Expect is also the name of a program used to automate interactive applications, by scripting responses to prompts.

See also: expectation, probability theory, forecast.