The Pharisees were a social movement and a school of thought in the Holy Land during the time of Second Temple Judaism. After the destruction of the Second Temple in 70 CE, Pharisaic beliefs became the foundational, liturgical and ritualistic basis for Rabbinic Judaism.
The New Testament, particularly the Synoptic Gospels, presents especially the leadership of the Pharisees as obsessed with man-made rules (especially concerning purity) whereas Jesus is more concerned with God’s love; the Pharisees scorn sinners whereas Jesus seeks them out.
Because of the New Testament’s frequent depictions of Pharisees as self-righteous rule-followers, the word “pharisee” (and its derivatives: “pharisaical”, etc.) has come into semi-common usage in English to describe a hypocritical and arrogant person who places the letter of the law above its spirit.