I was reading the Green Mile by Stephen King and when John Coffey shook his head in answer to questions it was implied that the word "nod" referred to the lowering and raising of his head in affirmation and the moving of his head side to side is negatory. Is this correct in usual speech? I thought to shake ones head was ambiguous and could mean "yes" or "no"?
Head movements vary in their meaning depending on the culture in question. In general, in countries where English is the native language, a "nod" (not a "node") is an up and down movement of the head meaning "yes." A head shake is a side to side movement meaning "no." At least for most English speakers in Britain and America, a nod never means no, and a shake never means yes. This is somewhat oversimplified and variations exist, but for the most part, the basic pattern is as I have stated it.
I would agree with the response that indicated that a "nod" or movement of head up and down means "yes" in most English speaking cultures and a "shake"; side to side movement of head indicates "no." However, there appears to be regional differences in the US. While I grew up in the Northeast, I also lived in the South; and there I often heard the expression "shake your head 'yes' if you agree". But in those instances the person would be meaning what I would call "nod" the head; as in up and down. One in the South would also say, "Shake your head 'no'"; meaning move the head from side to side. So, there appears to be a different interpretation of "shake your head" regionally.