My understand ingis :

Face sitting (or Queening) is a practice whereby the Top (Dominant who may be female or male) sits on the face of the Bottom (submissive), who may be restrained or not, and forced the bottom to do cunnilingus and/or anilingus.

Smothering implies that not only will there be Face sitting, but it will include breath control, also.  Breath control being any practice in which a person's breathing is constricted or interrupted, as with a hand or ligature around the throat or with a covering over the face, for the purpose of increasing sexual arousal or sexual climax.

Smothering may include a SmotherBox which is a lockable box, often padded with leather, designed to be locked over the head of a Bottom (submissive)  which has a large opening that exposes the submissive's face, allowing the Top (Dominant) to straddle or sit on the box. The Box may include a mechanism for affixing the box to the floor or to an item of furniture such as a bed or bench, so that the submissive can not move.


In all practices of BDSM, definitions are more like guidelines.  YOU MUST ASK THE PERSON YOU PLAY WITH WHAT THEIR UNDERSTANDING OF A WORD OR PRACTICE IS.

A good example of this is the term Edge Play.  Some people swear it means only the use of a knife or blade, some incorporate anything that may be dangerous to your health, such has erotic asphyxiation.


Have Fun.  Be Safe,


~a

In my experience, when a client asks for face-sitting, he always wants me naked.  Smothering, they usually want me clothed.  

Not sure if this is the standard dividing line between the two, but it's what I've noticed in my experiences.