The document defines expected value as the sum of each possible value of a random variable multiplied by its probability. For a random variable X that can take on values x1, x2, x3, etc. with probabilities p(x1), p(x2), p(x3), etc., the expected value is defined as E(X) = ∑ xk p(xk). An example is provided calculating the expected value of Y, the number of microcomputers getting out of order per year at a university, which is determined to be 1.4 based on the given probabilities.