What is the definition of non ferrous materials?

Ferrous (Fe) is actually iron. Material with less than 50% iron is a non-ferrous material or alloy. Material with 50% or more iron is a ferrous material or alloy.

Ferrous materials contain iron and non-ferrous do not

definition for nonmagnetic materials

Yes. Plastic is not nor contains iron, so it is not ferrous.

Ferrous - containing, pertaining to or made of iron. Nonferrous therefore is an adjective meaning that does not contain or pertain to the element iron.