1. The upper region of the earth's atmosphere between the troposphere and mesosphere, from 6 miles or 10 kilometers to 30 miles or 50 kilometers above the earth's surface: Modern passenger aircraft are designed to fly in the stratosphere where there are no clouds.

The stratosphere has no clouds and consists of gradual temperature increases.

2. In former use, it referred to all of the atmosphere above the troposphere.
3. A very high or the highest level or position.
4. The nearly uniform cold ocean water masses in high latitudes and near-bottom waters of middle and low latitudes; ocean water below the thermocline.