Mediation (statistics) – Wikipedia
Cites the classic paper:
Baron, R. M. and Kenny, D. A. (1986) “The Moderator-Mediator Variable Distinction in Social Psychological Research – Conceptual, Strategic, and Statistical Considerations”, Journal of Personality and Social Psychology, Vol. 51(6), pp. 1173–1182.
https://en.wikipedia.org/wiki/Mediation_(statistics)