Statistic, a singular noun, has three meanings: (1) an observed number or event, (2) a mathematical operation (and the resulting number) performed on sample data, and (3) an operation (and the resulting number) obtained from a sampling distribution. The plural form for each of these three cases is statistics. A fourth meaning of the word statistics is a branch of mathematics devoted to the analysis, interpretation, and presentation of empirical data. Statistics, as a branch of mathematics, is a singular noun. In most contexts statistic (with an s) refers to this branch of mathematics, which scientists and others use to analyze data from empirical studies.

In conversational use, statistic means a single number or a single event. The 84 in 84 people attended the reunion is ...