significant

Significant is an adjective with several related senses. In general use, it means meaningful or important enough to be worthy of attention or to have consequences. It can describe events, results, or relationships that carry meaning beyond the ordinary.

In statistics, significance refers to the degree to which an observed effect is unlikely to be due to chance under a null hypothesis. A result is statistically significant when its p-value falls below a prechosen threshold, commonly 0.05. Significance testing does not measure the size of an effect; a result can be statistically significant but practically or scientifically insignificant, especially in large samples.

In measurement, the term is connected to significant figures (significant digits), which are the digits that contribute to the precision of a value. The rules distinguish which zeros are significant; for example, 0.00450 has three significant figures, while leading zeros are not counted.

Etymology and related terms: significant derives from Latin significare “to mark, indicate,” via Old French significatif. The root sign- means mark, and -ficare means to make or do, reflecting the sense of making meaning or indicating importance.

Usage notes: In everyday language, the phrase significant other refers to a person with whom one has a substantial relationship; the term emphasizes importance rather than formal status. In science and policy writing, careful distinction is maintained between statistical significance and practical or clinical significance.