Thank You for this.  I needed to see that word. From Wikipedia:   A shibboleth (/ˈʃɪbəlɛθ, -ɪθ/ (About this soundlisten))[1][2] is any custom or tradition, usually a choice of phrasing or even a single word, that distinguishes one group of people from another.[3][4][5] 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. ... The term shibboleth can be extended, as in the discipline of semiotics, to describe non-linguistic elements of culture such as diet, fashion and cultural values. Cultural touchstones and shared experience can also be shibboleths of a sort. For example, people about the same age who are from the same nation tend to have the same memories of popular songs, television shows, and events from their formative years. One-hit wonders prove particularly distinctive. Much the same is true of alumni of a particular school, veterans of military service, and other groups. Discussing such memories is a common way of bonding. In-jokes can be a similar type of shared-experience shibboleth.  [bolding is mine]