If the document is a research paper on mechanics, it probably deals with the , used to predict when metals will begin to deform permanently (yield).
Strategies for minimizing secular J2 effects in satellite formations. j2.pdf
Practical applications in finite element analysis for testing the durability of metal components. If the document is a research paper on
How to apply for an Employment Authorization Document (EAD) to legally work while in the country. it probably deals with the
Modern extensions, such as combining J2 plasticity with damage concepts to account for stiffness degradation.