The document defines anatomical position and describes the three main planes of the body - median sagittal, coronal, and horizontal. It explains that anatomical position refers to standing erect with arms at the sides and palms facing forward. The body has three imaginary planes that divide it into sections at right angles: median sagittal divides the body into left and right halves, coronal divides it into anterior and posterior parts, and horizontal divides it into upper and lower parts. Terms like anterior, posterior, proximal, distal are also defined in relation to anatomical position and body planes.