What term describes the visible luminous body of gases that is burning?

The term that describes the visible luminous body of gases that is burning is "flame." A flame is produced when a combustible material undergoes combustion, resulting in both heat and light. This visible manifestation of burning typically appears as a flickering or steady glow, depending on the conditions of the fire, such as the type of fuel and the presence of oxygen.

Flames consist of hot gases that emit light due to the excitation of particles during combustion, which is why they can be seen. The color and characteristics of a flame can vary based on different variables, including the type of material being burned and the temperature of the combustion process. Understanding the nature of flames is crucial in fire behavior studies, as it relates to how fires start, spread, and can be controlled or extinguished.

In contrast, the other options refer to different phenomena associated with combustion but do not encapsulate the idea of a burning body of gases in the same way that "flame" does. Fumes refer to smoke or vapor produced by burning substances, vapor is a state of matter describing gases (particularly from liquids), and smog is a form of air pollution that includes a mix of smoke and fog, but not specifically a burning entity like a flame.