Question

z English zoo, buzz, has, easy. Spanish typically do not have this sound, but some dialects turn s to [z] when it comes before an voiced consonant: mismo, musgo, desde.

Accepted Answer

Voiced Alveolar Fricative http://en.wikipedia.org/wiki/Voiced_alveolar_sibilant

Symbol	z
Name	Voiced Alveolar Fricative
Notes	English zoo, buzz, has, easy. Spanish typically do not have this sound, but some dialects turn s to [z] when it comes before an voiced consonant: mismo, musgo, desde.
Ref	http://en.wikipedia.org/wiki/Voiced_alveolar_sibilant

S Z Voiced Alveolar De Fricative English Oo