Effect size
Short definition
Effect size is a measure of the magnitude of a difference or association found in a study, indicating how large the effect is, not just whether it is statistically significant.
In plain language
A result can be statistically significant and still be of little practical importance, especially in large studies. Effect size answers «how much?». A common measure is Cohen's d, for which Cohen proposed the rough benchmarks of 0.2 (small), 0.5 (medium) and 0.8 (large). In meta-analyses of virtual reality and pain, results are often reported this way, as a standardised mean difference.