Posture is the position in which you hold your body upright against gravity while standing, sitting, or lying down. The position of your spinal column is reflected in your posture.
Proper posture keeps bones and joints in the correct alignment so that muscles are being used properly. Proper posture is also more energy efficient and can lead to better overall performance.
To demonstrate what proper posture looks like
If viewing from behind. The ears, shoulders and hips should be level. The feet should be pointing forward.
If viewing from the side. The ear, middle shoulders middle of the hips and the ankle bone should be aligned