Voice or voicing is a term used in phonetics and phonology to characterize speech sounds (usually consonants). Speech sounds can be described as either voiceless (otherwise known as unvoiced) or voiced.
The term, however, is used to refer to two separate concepts:
For example, voicing accounts for the difference between the pair of sounds associated with the English letters "s" and "z". The two sounds are transcribed as [s] and [z] to distinguish them from the English letters, which have several possible pronunciations, depending on the context. If one places the fingers on the voice box (i.e. the location of the Adam's apple in the upper throat), one can feel a vibration while zzzz is pronounced but not with ssss. (For a more detailed, technical explanation, see modal voice and phonation.) In most European languages, with a notable exception being Icelandic, vowels and other sonorants (consonants such as m, n, l, and r) are modally voiced.