Cohen's d is a measure of effect size that assesses the difference between two means in terms of standard deviation units. It helps determine the practical significance of the observed difference.
Effect Size: A quantitative measure of the strength of a phenomenon, used to assess practical significance.
$t$-test: A statistical test used to compare the means of two groups to determine if they are significantly different from each other.
$p$-value: The probability that observed data would occur by random chance; used to determine statistical significance.