What is the name of the waxy coating that keeps plants from drying out?

Cutin

Explanation:

The cuticle is composed of cutin, a wax-like material that is a hydroxy fatty acid and fills in spaces in a plant's epidermis, or outermost layer of cells. The cuticle prevents too much of the water from the plant's interior from escaping, protecting the plant from drying out.

The waxy layer that keeps plants from drying out is called cutin.