Final answer:
The lower concave area of the lung is known as the hilum, which serves as the site on the mediastinal surface where the lung connects to blood vessels, lymphatic vessels, nerves, and bronchi.
Step-by-step explanation:
The lower concave area of the lung is termed the hilum. This structure on the mediastinal surface of the lungs where major elements such as blood vessels, lymphatic vessels, nerves, and a bronchus enter and exit the lung. The hilum plays a crucial role in connecting the lungs to the rest of the body, ensuring that they receive the necessary blood flow and nervous input, as well as a passage for the air through the bronchi. Each lung has its own hilum, which can be seen as a key gateway for the organ's function. The lungs are suspended within the pleural cavity of the thorax, and the hilum contributes significantly to their proper placement and attachment within the chest cavity.