These planes divide the human body, as well as organs and other body parts, into different sections to describe an organ or limb’s location, structures in organs and limbs, and or the movements of body parts. The three planes are orthogonal, so the short answer to the question in the title is 90°.
The sagittal or lateral plane dives the body into left and right halves and is an x-z plane. Technically, the sagittal or median plane goes right through the middle between the body’s left and right halves. Planes parallel the sagittal planes are called parasagittal planes. It is called the sagittal plane because it goes through or is parallel to the sagittal suture, the line running along the top of the skull that marks where the left and right halves of the skull grew together.
The coronal or frontal planes divide the body into front and back (also called dorsal and ventral or posterior and anterior) sections and are x-y planes.
The transverse planes, also known as the axial or horizontal planes, are parallel to the ground and divide the body into top and bottom parts. The top and bottom sections also called the superior and inferior section s or the cranial (head) and caudal (tial) sections). They are x-z planes.