I’ve run across the incorrect descriptions of these two actions far too many times for it to be coincidental anymore, so today let’s define them.
The action that can be described in the above photo is nodding. Dear 10th Doctor David Tennant is nodding his head in response to something that was said to him. Nodding, the up-and-down motion of the head, is used to indicate affirmation, a positive response, a yes in body language.
In THIS photo, DT is moving his head from side to side, or shaking his head. This motion indicates denial, a negative response, or no in body language.
This is basic body language 101. If you write that your character shakes his head yes to something… that’s incorrect. He NODS his head for yes and SHAKES his head for no.