Final answer:
A cross-sectional section, also known as a transverse plane, is a horizontal cut through an organ at right angles to the long axis, dividing it into upper and lower parts.
Step-by-step explanation:
A cut through an organ at right angles to the long axis is known as a cross-sectional section. This type of cut is referred to in anatomical terms as a transverse plane or horizontal plane. The transverse plane divides the body or organ into upper and lower portions and is perpendicular to both the sagittal planes and the long axis of the body. In contrast, other types of anatomical planes include the midsagittal plane, which divides the body into equal right and left halves, and the frontal or coronal plane, which separates the anterior and posterior portions of the body.