It's a religion, cupcake. You're confusing being Jewish with Judaism.
Some, but by no means all Jews come from a particular ethnic or cultural group in which the religion aligns with an ethnic or cultural identity, and those groups are sometimes endogamous (marrying only within the group), and Jewishness - but not Judaism - is believed to be inherited from one's parents.
A person can be Jewish by birth or conversion, but Judaism is a religion.
One thing it is not is a "race."