The Pharisees were a Jewish movement that existed during the Second Temple period, characterized by an encyclopedic knowledge of the Hebrew Scripture and a fixation with the minutiae of said scripture as a means of understanding God's will. For example the scripture required tithing — giving 10% of income, or yearly increase — to the priesthood. Pharisees went to the trouble of counting the seeds and leaves of the plants in their garden and tithing on those amounts.
The New Testament describes them in invariably negative terms. According to Christian tradition, the Pharisees sought harsh penalties for the smallest of infractions, and, like all fanatics, considered themselves far more important than everyone else. As a result, the term pharisee is considered an insult in Western culture, generally meaning a hypocritical, self-righteous nitpicker.
However, the Pharisees were also one of the most prominent sects of Judaism due to their emphasis on scriptural knowledge and interpretation, and were also the ones most directly responsible for the creation of the immense body of theological commentary known as the Talmud (as well as Rabbinic Judaism as a whole) as a way to preserve Jewish identity after the destruction of the Second Temple and the last vestiges of the Judahite temple-state. The traditional Jewish emphasis on learning and study from medieval to modern times is therefore a direct positive legacy of Pharisaic influence.