The respiratory tract is a general term that is used to describe all the parts of the body that are involved in helping a person to breathe. Health professionals generally make a distinction between the upper respiratory tract and the lower respiratory tract.
The upper respiratory tract consists of the nose, the sinuses, the mouth, the throat, the pharynx and the larynx. The lower respiratory tract consists of the trachea (windpipe), the bronchi (the two branches that the trachea divides into as it enters the lungs), bronchioles (the tiny airways that are found throughout the lungs) and the alveoli (tiny air sacs at the end of the bronchioles)
Definition from NHS Choices: Respiratory