What is the wing span in aspect ratio's calculation? We all know that the aspect ratio of an airplane is calculate as:
$$AR=\frac{b^2}{S}$$

Where:

$AR=$ Aspect ratio

$B=$ Wingspan

$S=$ Wing's area

In an airplane, wing span is the distance from tip to tip of the wing. That means the fuselage also calculated. Below are two picture of two different kind of airplane: Boeing and Cessna. As you see, the wing is placed in different position. The Boeing is below of the fuselage so it look like integrated to the wings. But the Cessna is placed on top of the fuselage, make the fuselage is like the separator of the two wings rather the integrator.
 


But in another time, what we call wing is a thing that is attached to the fuselage. The picture below shows what the wing span is. The fuselage itself is not considered as part of wing.



To avoid miscalculation, I would like to know what is exactly b in that equation. For this case, just consider the wing shape is fully rectangle. Appreciate if with reference.
b is the width of the wing's projection on the horizontal plane, from tip to tip. The wing's vertical position on the fuselage does not influence b. This may or may not include winglets and ideally should be clarified when b is specified.

Calling one half of the wing a wing is sloppy use of language. Ideally, a wing half should be called that, and not be confused with a wing.