Question

β Like [b], but with the lips not quite touching. In Spanish b and v are pronounced this way unless they come after a nasal consonant or at the beginning of an utterance (grupo fónico).

Accepted Answer

Voiced Bilabial Fricative http://en.wikipedia.org/wiki/Voiced_bilabial_fricative

Symbol	β
Name	Voiced Bilabial Fricative
Notes	Like [b], but with the lips not quite touching. In Spanish b and v are pronounced this way unless they come after a nasal consonant or at the beginning of an utterance (grupo fónico).
Ref	http://en.wikipedia.org/wiki/Voiced_bilabial_fricative

Bilabial Fricative β Voiced B Lips Touching Spanish