Shibboleth

A shibboleth () was originally a single word which distinguished one group from another.
Rather more widely, it is any custom or tradition that distinguishes one group of people from another. Shibboleths have been used throughout history in many societies as passwords. They are simple ways of self-identification: they signal loyalty and affinity.
Origin.
The term comes from the Hebrew word "shibbólet" (), which means the part of a plant containing grain, such as the head of a stalk of wheat or rye. 
The modern use comes from an account in the Hebrew Bible. How this word was pronounced was used to distinguish friend from foe. In the Book of Judges, chapter 12, the inhabitants of Gilead inflicted a military defeat on the invading tribe of Ephraim (around 1370–1070 BC). The surviving Ephraimites tried to cross the River Jordan to their home territory, but the Gileadites secured the river's fords to stop them. 
To identify and kill the Ephraimites, the Gileadites told each suspected survivor to say the word "shibboleth". The Ephraimite dialect resulted in a pronunciation that, to Gileadites, sounded like "sibboleth". In the King James Bible: 
The concept of a shibboleth is still with us. It is any word, phrase, jargon or pronunciation which identifies a person as a member of a particular group.