Troposphere: the region of the atmosphere closest to the Earth

The troposphere extends from the surface up to about 10 km in altitude, although this height varies with latitude. Almost all weather takes place in the troposphere. Mt. Everest, the highest mountain on Earth, is only 8.8 km high. Temperatures decrease with altitude in the troposphere. As warm air rises, it cools, falling back to Earth. This process, known as convection, means there are huge air movements that mix the troposphere very efficiently.

The lowest layer of the Earth's atmosphere, extending from the ground to the stratosphere at approximately 13 km of altitude. In the troposphere, temperature decreases with height.

The lower atmosphere, to a height of 8-15 km above Earth, where temperature generally decreases with altitude, clouds form, precipitation occurs, and convection currents are active. See atmosphere.
NASA Earth Observatory

Troposphere - The lowest layer of the Earth's atmosphere, ranging from the ground to the base of the stratosphere with a altitude of 10-15 kilometers depending on the latitude. This is where all weather occurs. The word troposphere is derived from the Greek words tropos--turning and spharia--sphere. 
Atmospheric Chemistry Glossary