What is the term for a variable that affects the relationship between two other variables?

A moderator variable is a type of variable that influences the strength or direction of the relationship between two other variables. It can either amplify or diminish the effect of one variable on another, providing insight into the conditions under which the relationship holds true. For instance, if you're studying the impact of stress on academic performance, a moderator could be social support; the relationship might be stronger for individuals with low social support than for those with high social support.

The other options describe different roles within research. A dependent variable is the outcome that researchers aim to explain or predict, and it is influenced by the independent variable. The independent variable is the variable that is manipulated or controlled to determine its effects on the dependent variable. A mediating variable accounts for the process or mechanism through which the independent variable affects the dependent variable, essentially acting as a bridge in that relationship rather than altering it like a moderator does.