Divergence in the atmosphere is best defined as:

An air that moves out of an area

Explanation:

The divergence in the atmosphere refers to the air that moves out of an area. In simple words, it means the horizontal outflow of air.

This divergence of air takes place in the atmosphere due to the movement of a much stronger wind away from a comparatively weaker wind. In the upper atmosphere, the divergence of air results in the uplifting of air and the speed at which these air moves upward directly depends upon the magnitude of divergence. It also depends on some of the other uprising and sinking mechanisms.

The answer is (Air moving out of an area!)