Made with both lip
s together: as opposed to labiodental
, made with upper teeth on lower lip.
Bilabial sounds in English are B, P, and M. Other sounds that can be bilabial are F and V: for example the Spanish letters B and V between vowels (not initially) are a weak bilabial V sound. The Japanese F in Fuji (which is really just the form of H used before U) is bilabial.
B, P, and M are always bilabial; F and V depend on the language, sometimes being bilabial and sometimes being labiodental (as in English and French). It is rare to find both kinds in one language, but examples are southern African languages such as Venda, in which their people are called Vhavenda. Here the VH represents the bilabial V.
One Solomon Islands language has a bilabial roll, which is the BRR sound you make to express cold.
W (with its English sound) has double articulation: it is simultaneously bilabial and velar.
As far as I know every language in the world has bilabial sounds. Almost all have both P and M. Arabic lacks P, some from British Columbia lack M.
The phonetic symbols for the bilabial sounds are [p] [b] [m], with straightened forms of the Greek letters [φ] [β] for the fricatives, and small capital [B] for the roll.