Final answer:
The transverse plane is an imaginary line that divides the body horizontally into upper and lower portions.
Step-by-step explanation:
The imaginary line that divides the body horizontally into an upper and lower portion is called the transverse plane. This plane produces images referred to as cross sections. It is one of the three planes commonly used to divide the body, with the other two being the sagittal plane (divides the body vertically into right and left sides) and the frontal plane (divides the body into front and back portions).