1. A situation in which a language exists in two forms, one formal or literary and the other informal, and a person uses the form which is appropriate for a particular situation.
2. The existence of a formal literary form of a language, considered more prestigious, along with a colloquial form used by most speakers and considered to be a lower status.
3. A sociolinguistic phenomenon in which complementary social functions are distributed between a prestigious or formal variety and a common or colloquial variety of a language; such as, in Greek, Tamil, or Scottish English.
4. In medicine, a form of schistoglossia in which the lateral lingual swellings fail to fuse, producing a bifid tongue or one with a lengthwise cleft.