Communication not directly involving the head or, by extension, the body. This includes any form of internet chat aswell as, technically, letters. The significance of it is that the lack of emotion and tone inputs into decapitated conversations can cause serious miscommunications. A simple example is the difficulty of conveying sarcasm via writing. While not impossible, it is much more difficult than when talking to someone. Importantly, decapitated communication is not the same as long distance communication, as many luddites will have you believe. Video chatting, for instance, is not decapitated. Neither is simply talking on the phone. In both of these cases, there is direct input of the head - in the case of the phone, it is only voice but it is still sufficient to make communication much more seamless.
Emoticons were a noble attempt at overcoming the barriers of decapitated communication, despite achieving only limited success.
The limitations of decapitated communication make discussions about emotional situations, such as relationships, clumsy and often unsuccessful. It is because of decapitation that such conversations can often take a turn for the worse.