Here's a bried definition from theopedia of the New Perspective on Paul.
"The New Perspective on Paul, also called New Perspectivism (hereafter NPP) is a system of thought in New Testament scholarship that seeks to reinterpret the Apostle Paul and his letters. In brief, the NPP is a reaction to the Lutheran Paul (i.e. the traditional interpretation of him). Proponents of the "Lutheran Paul" understand him to be arguing against a legalistic Jewish culture that seeks to earn their salvation through works. However, supporters of the NPP argue that Paul has been misread. He was actually combating Jews who were boasting because they were God's people, the "elect" or the "chosen ones". Their "works", so to speak, were done to show they were God's covenant people and not to earn their salvation. The result is a Judaism that supposedly affirmed sola gratia (grace alone). Presently, its effects are seen in the academic world of New Testament scholars, particularly those who focus their attention on Pauline studies and the study of first century Judaism."
[HT: Between Two Worlds]