Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Tracheoesophageal fistula ?
    ### Response:
    Tracheoesophageal fistula (TEF) is a life-threatening condition in which there is an abnormal connection between the esophagus and trachea (windpipe). The esophagus and trachea run next to each other through the chest cavity. The esophagus carries food and saliva to the stomach, while the trachea carries air to the lungs.
    