Any two sounds, in the same language or in different languages, which fit the same description in terms of articulatory phonetics, are said to be instances or recurrences of “the same” ‘speech sound’. This renders the term “speech sound” relative, since our articulatory description may be either loose or precise.
- Hockett (1958), a pag.24

Speech sounds can be described in terms of the bodily motions, called ‘articulation’, that produce them.
- Hockett (1958), a pag.62