Bilabial sounds involve both lips as the articulators. (If you wanted to be hyper-consistent about always having an active and a passive articulator, you could say that the lower lip is the active articulator and the upper lip is the passive. The lower lip does usually move more than the upper lip when making a bilabial sound, but the upper lip moves too, so it's not really "passive".)

The English bilabial sounds are [p], [b], and [m].

Vocal tract state for [p] and [b]
[p] or [b]

It's possible to make bilabial fricatives by not closing the lips completely and leaving an opening narrow enough to cause turbulent airflow. To English speakers, these sound like [f] and [v].

Languages where bilabial and labiodental fricatives are contrasting sounds are rare. Ewe (Niger-Congo, Ghana and Togo) is one:

[ɸu]    'bone'      [fu]    'feather'
[βɔ] 'python'   [vɔ] 'to be finished'

As we've seen, one of the two articulations involved in [] is lip rounding (which can be described as a bilabial approximant).

bilabial trill

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