Definitions for "Yield point"
That point, or intensity of stress, at which the rate of stretch begins to increase rapidly.
Can be defined as the point where a tensile test piece begins to extend permanently. If the load is reduced to zero, the test piece will not return to its original length.
Yield Point is the first stress in a material (less than the maximum attainable stress) at which an increase in strain occurs without an increase in stress. ASTM D1621