(medicine) A rule for clinical trials used for determining the rate of adverse side effects when no such side effects present during the course of the trial.
(rhetoric) A rule which states that things which come in groups of three are inherently funnier or more effective than things which come in groups of other sizes.
(rhetoric) Specifically, the technique of having a setup in advance, a reminder to keep it fresh in the audience's memory, and then a payoff.
(religion) A religious tenet stating that the energy a person puts out into the world, positive or negative, will be returned to that person three times.
