Final answer:
A large body of air with high temperature and high relative humidity is known as a maritime tropical (mT) air mass, characterized by its moist and warm properties.
Step-by-step explanation:
If a large body of air has a high temperature and a high relative humidity, then the air mass is called maritime tropical (mT). This type of air mass originates over warm ocean waters and carries both heat and moisture. Air masses are characterized by their moisture content and temperature, with the prefix 'maritime' (m) indicating that the air mass is moist because it forms over water, and 'tropical' (T) indicating that it has formed in a region with high temperatures. Other air mass types include continental polar (cP), continental tropical (cT), maritime polar (mP), and continental arctic (cA); each brings distinct weather patterns due to their unique temperature and humidity characteristics.