A material is said to be ductile if it

A material is said to be ductile if it can be stretched thin when tensile stress is administered. Such a material can be stretched into a wire.

This is different from malleability which describes a material that can bend or alter shape using compressive force e. g. hammering, rather than tensile stress.

Tensile stress is a type of force or stress that alters the length of a material in the same direction as the force being applied.

The opposite of ductile is brittle. Brittle materials can break when subjected too much tensile stress.