열 (Heat) is a form of energy that is transferred between systems or objects with different temperatures. It flows from the hotter object to the cooler one until thermal equilibrium is reached. This transfer can occur through conduction, convection, or radiation, and is essential in various natural processes and technologies. In everyday life, 열 is experienced when touching a hot stove or feeling the warmth of the sun. It plays a crucial role in many scientific fields, including thermodynamics, which studies the relationships between heat, work, and energy. Understanding 열 helps us harness energy efficiently and improve our daily lives.