To go in the reverse direction.

“the train backed into the station;  the horse refuses to back”

To support.

“I back you all the way;  which horse are you backing in this race?”

(of the wind) To change direction contrary to the normal pattern; that is, to shift anticlockwise in the northern hemisphere, or clockwise in the southern hemisphere.

Support, especially financial.

“It's a volunteer organization that works with backing from the city and a few grants.”

A liner or other material added behind or underneath.

“The cardboard backing gives the notebook a little extra stiffness.”

A backdrop.

Providing support for the main performer.