1, expected to be a definite number, obtained according to the probability distribution. Whether the experiment is carried out or not, we can get the expectation. Mathematical expectation, also known as mean, refers to the average value of random variables. This average refers to the weighted average with probability as the weight.

2, the average (mean), is the average of the sum after doing many experiments.

In probability theory and mathematical statistics, mathematical expectation (or simply mean, or expectation) is the sum of the possible results multiplied by the results in each experiment, which is one of the most basic mathematical characteristics. It reflects the average value of random variables.

It should be noted that the expected value is not necessarily equal to the common sense "expectation"-"expected value" is not necessarily equal to every result. The expected value is the average of the output values of variables. The expected value is not necessarily contained in the set of output values of variables.

The law of large numbers stipulates that as the number of repetitions approaches infinity, the arithmetic average of numerical values almost inevitably converges to the expected value.