A Cohen is one of the class of priests among the Jewish people. Membership is hereditary, via the father. A slew of common Jewish surnames (Cohen, Kagan, Kahane etc) are variations of Cohen and usually indicate that the holders are Cohanim.
Cohen simply means priest in biblical Hebrew (as well as in Canaanite and Ugaritic). However, Chief Rabbi Sacks has argued persuasively that the primary meaning of Cohen was teacher. Just before the Torah is given, God promises that Israel will
be a kingdom of priests (Exodus 19:6). This is an aspiration to universal literacy according to Rabbi Sacks; in the ancient world, only the priests could read.
The priests performed their full range of functions when the Temple stood. Today, the rights and duties of Cohanim include being called up for the first aliyah to the Torah and giving the community the priestly blessing in synagogue ("May the Lord bless you and keep you" etc, Numbers 6: 24-25).
