An estimate of a population parameter, such as a sample mean or sample proportion, is different for different samples (of the same size) taken from the population. Sampling error is one of two reasons for the difference between an estimate and the true, but unknown, value of the population parameter. The other reason is non-sampling error.
Curriculum achievement objectives references
Statistical investigation: Levels (5), (6), (7), (8)
Statistical literacy: Levels 7, (8)