Anteroposterior Axis refers to the axis that has the same directional orientation as the sagittal plane of motion and runs from front to back at a right angle to the frontal plane of motion. It is the axis perpendicular to the frontal plane, locating horizontally from the front (anterior) to the back (posterior) and parallel to the ground.
Anteroposterior Axis is also known as the sagittal or AP axis.