Stance:
There isn't any technical definition for stance of the bike,. But it can be said that it is the general outline of a bike which defines it's purpose and style.
Stance of a bike does not mean the seating position of the rider. That is Riding stance. Riding stance is shown by the triangle that we have seen before.
Stance is majorly shown by front fairing position,tank and tail piece. Stance generally makes the bike feel aggressive or gentle. Ducatis have a relatively upright stance. The headlight fairing is higher from the tyre. The tank and the tail are in somewhat same line.The tank peak is rear biased. The Japanese bikes have an aggressive stance. The fairing is much closer to the front wheel. The tail is very high pointing upwards. And the tank peak is usually directed towards the front part.
In the following example, we see that how the stance of the Kawasaki Z1000 changed with time. How upright it was and how slanted it is now.
Just checkout the peak of the tank! So,higher the peak, the more muscular the bike looks.
Nowadays there is an increased trend towards aggressive design. All of the other types,namely cruisers,tourers,etc are moving towards forward inclined sports styling.