The region of the stress-strain curve in which the material returns to the undeformed state when applied forces are removed is called the elastic region.
The region in which the material deforms permanently is called the plastic region.
The point demarcating the elastic from the plastic region is called the yield point. The stress at yield point is called the yield stress.
The permanent strain when stresses are zero is called the plastic strain.
The off-set yield stress is a stress that would produce a plastic strain corresponding to the specified off-set strain.
A material that can undergo large plastic deformation before fracture is called a ductile material.
A material that exhibits little or no plastic deformation at failure is called a brittle material.
Hardness is the resistance to indentation.
The raising of the yield point with increasing strain is called strain hardening.
The sudden decrease in the area of cross-section after ultimate stress is called necking.