What term is used to describe the layers of the atmosphere where aircraft typically fly?

The troposphere is the correct term used to describe the layers of the atmosphere where most aircraft typically operate. This layer extends from the Earth's surface up to about 8 to 15 kilometers (5 to 9 miles) high, depending on geographical location and weather conditions.

In the troposphere, the temperature generally decreases with altitude, creating the conditions that support weather phenomena such as clouds, rain, and storms. Most commercial flights take place in this layer because it allows for optimal lift and navigation, as the air is dense and conducive to flight.

While the stratosphere, which lies above the troposphere, is also a significant layer in aviation (especially for high-altitude flights like some jetliners and military aircraft), the majority of commercial air traffic operates within the troposphere. The other layers, such as the mesosphere and thermosphere, are primarily too high for conventional aircraft to reach, with very low air density and extreme temperatures that are unsuitable for flight.