What is the Meaning of "PIECEWISE" in LS-Dyna material MAT_24 (MAT PIECEWISE LINEAR PLASTICITY)

Mat_24 has 8 EPS-ES (Eq. Plastic. Strain - Yield Stress) pairs that you can optionally assign values to, in order to define a stress-strain curve consisting of up to 8 linear segments. This is what PIECEWISE refers to. In essence, you have the capability of approximating a realistic non-linear stress-strain behavior by a sequence of linear segments (up to 8 in total), hence the term 
PIECEWISE.