Final answer:
An air mass is a large body of air that usually has uniform characteristics of temperature and humidity. It forms over regions with consistent surface conditions and can cover thousands of square kilometres.
Step-by-step explanation:
A large body of air that usually has uniform characteristics of temperature and humidity is called an air mass. An air mass is a large volume of air that has similar temperature and humidity throughout. Air masses form over regions with consistent surface conditions and can cover thousands of square kilometers. They are classified based on their temperature and humidity characteristics, such as warm and humid, cool and dry, and so on.