noun /ˌɪd.i.əʊˈsɪŋ.krə.si,ˌɪdi.əˈsɪŋkɹəsi/
a) A behavior or way of thinking that is characteristic of a person.
He mastered the idiosyncrasies of English spelling.
b) A language or behaviour that is particular to an individual or group.
Wikipedia foundation.