Labialisation
Labialisation is a secondary articulatory feature of phonemes in a language, most usually used to refer to consonants. Labialisation, simply put, is the usage of the lips as a secondary articulator while the remainder of the oral cavity produces some other phoneme.While labialisation is by no means universal in the world's languages, it is certainly extremely widespread. It appears in families as varied as Northwest Caucasian, Athabaskan, Salishan and (from a diachronic perspective) Indo-European, where it is thought that the proto-language, Proto-Indo-European, used labialised velar consonants, and Minoan Greek appears to have used it as well.
Labialisation is not restricted to lip-rounding, although this is certainly the most common type. The following labial articulations have been found as realisations of labialisation:
