When a system of forces act on a body, it undergoes some deformation. This deformation per unit length is known as unit strain or simply a strain.
Mathematically
Strain = (Change in Length)/(Original Length)

Primary Strain or Linear Strain The deformation of the bar, per unit length in the direction of the force is known as primary or linear strain.
Secondary Strain or Lateral Strain Every direct stress is always accompanied by a strain in its own direction, and an opposite kind of strain in every direction, at right angles to it. Such strain is known as secondary or lateral strain.

Ductility is a property of a material enabling it to be drawn into wires.
Malleability is a property of a material enabling it to be drawn into thin sheets.

Hardness is a very important property of the metals and has a wide variety of meanings. It embraces many different properties such as resistance to wear, scratching, deformation and machinability etc. It also means the ability of the metal to cut another metal.
The hardness is usually expressed in numbers which are dependent on the method of making the test.

Ferrous Metals The Ferrous metals are those which have the iron as their main constituent, such as cast iron, wrought iron and steel.

Non-ferrous metals The non-ferrous metals are those which have a metal other than iron as their main constituent, such as copper, aluminium, brass, tin, zinc etc.