A sample is a subset of a population that is obtained through some process, possibly random selection or selection based on a certain set
of criteria, for the purposes of investigating the properties of the underlying parent
population. In particular, statistical quantities
determined directly from the sample (such as sample
central moments, sample raw moments, sample
mean, sample variance, etc.) can be used as
estimators for the corresponding properties of the
underlying distribution.

The process of obtaining a sample is known as sampling, and the number of members in a sample is called the sample
size.