In the Practice exam I did not understand the last question. what is the difference between estimate and estimator? Can you help me with that please. The answer says the Number is the estimator.....thanks

The formula we apply to determine the population number is represented by an estimator, but the numeric value is represented by an estimate. The mean symbol x bar, for example, is an estimator that equals the sample mean rule, but the value like: 20, is an estimate.