A
statistic (singular) is used to indicate the result of applying a statistical
algorithm to a
set of data. In the calculation of the
arithmetic mean, for example, the algorithm directs us to sum all the data values and divide by the number of data items. In this case, we call the mean a statistic. To be complete in describing any use of a statistic, one must describe both the procedure and the dataset.
The popular use of the term to mean a single measurement, or datum, differs from this meaning. A statistician would not call an individual person's height a statistic, but might use the term to refer in context to the median height of a group of people.
See also: statistics and statistical theory