Shibboleth

A shibboleth (/ˈʃɪbəlɛθ, -ɪθ/ ^ⓘ; Biblical Hebrew: שִׁבֹּלֶת, romanized: šībbōleṯ) is any custom or tradition, usually a choice of phrasing or even a single word, that distinguishes one group of people from another. Shibboleths have been used throughout history in many societies as passwords, simple ways of self-identification, signaling loyalty and affinity, maintaining traditional segregation, or protecting from real or perceived threats.