Shibboleth

A shibboleth is a custom or tradition, often a particular phrase or single word, that distinguishes one group of people from another. Historically, shibboleths have served as passwords, methods of self-identification, signals of loyalty or affinity, means of maintaining traditional segregation, or protection from threats. The term can also mean a moral formula held tenaciously and unreflectingly.

Definition

A custom or tradition that distinguishes groups

Historical uses

Passwords, self-identification, loyalty signals and protection

Extended meaning

A moral formula held tenaciously and unreflectingly