Smooth dancing refers to dances that travel around the floor (Foxtrot, Waltz, Tango, Viennese Waltz, etc.). The frame is what makes the two dancers "one". It is what allows the two 2-legged people to become a single four-legged entity. The frame is what "Lead and Follow" is all about. If there is no frame - there is no connection and no feeling.
In the Smooth dance frame, the bodies of the partners have the characteristics of the letter "Y" and the lady is off set to the man's right side (lady's belly button even with the man's right hip bone.). Your weight is slightly on your heels causing a backward feeling. The partnership has a "left side lead" (the left side of the body is slightly ahead of the right side). The Tango frame is slightly different (it has a right side lead and will not be discussed at this time). The man's right arm is connected to the lady between his wrist and elbow. The connection is with an upward pressure (never side pressure). This connection is with the muscle on the bottom of the lady's left upper arm as close to her body as possible. The man's left hand index finger (that is parallel to the floor) is at the eye level of the lady (regardless of the lady's height). It is always comfortable for the lady, not necessarily for the man. The Smooth frame feels very wide at the elbows. The man or lady's elbows are NEVER behind their bodies.
If you look at the dance frame from directly above and draw a line following the arms and bodies, you would draw an oval shape. The man and lady's head should NOT be inside the partnership's frame oval. The man and lady's head position are as if they were wearing bi-focal glasses and when looking past their partner they look through the bifocals and every thing is out of focus (this causes a raised head position). In partnership dancing, you do not see your partner, you feel your partner. The frame is consistently toned but never frozen and is moved by the movement of the body not by arm movements.
The lady is short from the shoulders down and tall from the shoulders up. Usually the lady will be shorter than the man but the lady NEVER dances "up" to the man no matter how tall. Stay down into the partnership's center. She will never be balanced in an "up" position. The man should bring his frame "down" to the lady.
Each person in the partnership has a center of gravity (usually about 2 inches below their belly button) and the partnership also has a center of gravity (somewhere between the partners). The goal of partnership dancing is to become "one" with your partner and that is accomplished by dancing through the partnership center of gravity. The connection to your partner is through the center (center of gravity) of the partnership even though the partnership is physically connected thought the frame above the center. The power of movement is initiated from your back through the partnership's center. The man's forward step feels like he is coming up underneath the lady.
I hope this description will give you a glimpse of what the Smooth frame is all about but as in all dancing you can not watch, as in this case read, and imitate.