Plain English Meaning
Because the Earth is spinning, anything moving over its surface — like a mass of air — appears to curve sideways instead of traveling in a straight line. In the Northern Hemisphere it curves to the right; in the Southern Hemisphere it curves to the left.
Full Definition
An apparent force, caused by the rotation of the Earth, that deflects moving air and other freely moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. It is not a true physical force but an effect observed because the Earth rotates beneath the moving object. Its strength increases with the speed of the object and with latitude, becoming zero at the equator and greatest at the poles.
Context Anchor
Seen in aviation weather discussions about wind direction, , and large-scale movement.