To what degree does social psychological research support the claim that non-verbal behaviour is a body language?

The study of non-verbal behaviour has always been a topic of great discussion, research and general debate. Due to this, non-verbal behaviour has stemmed a great deal literature, from which the significance of body language in interpersonal relationships has been employed. This has brought to light a great array of techniques or actions that can be seen to exemplify non-verbal behaviour, such as facial expressions, gestures and pose. These actions can be seen as silent communicators, having great influence over our social environment, in addition to conveying much greater detail about our mood, preference and true feelings than verbal communication alone….(short extract)