The head bobble, head wobble, or Indian head shake refers to a common gesture found in South Asian cultures, most notably in India. The motion usually consists of a side-to-side tilting of the head in arcs along the coronal plane. A form of nonverbal communication, it may mean "Yes", "Good", "OK" or "I understand", depending on the context.
In India the gesture is common in the certain parts, but may not be used consistently all around the country.
In India, this particular headshake can also be acknowledgement or encouragement. In the Western world, people often use a nod for the same purpose. It is not always associated with yes or no, and is actually used in place of no when the person doesn't want to say no.
In Bulgaria, this is the equivalent of a nod meaning yes, whereas a quick nod up means no.