Definitions for "Rule of three"
When selecting from a certificate of eligibles, an appointing officer must, with sole reference to merit and fitness, make a selection for the first vacancy from the highest three eligibles available for appointment on the certificate.
Structure of humor where two serious items set a pattern then the third unexpectedly switches the pattern which provokes laughter, or three jokes on one topic in a bit.
(See Learning Standard 16.8)The number three (3) recurs especially in folk literature and fairy tales. For example, three characters, three tasks, repetition of an event three times.