Judaism is the first Abrahamic faith to emerge and the progenitor faith from which Christianity and Islam emerged. One who subscribes to Judaism is known as a Jew. Judaism emerged over 3,000 years ago in what is now Israel where it remained largely isolated to until the Jews were exported as slaves and latter expelled over the course of the first century CE by the Roman Empire after a series of rebellions, causing Jewish enclaves to be established across Eurasia and Northern Africa. A key aspect to Judaism is that of Jewish Law, which is much more extensive and plays a much bigger role than Religious law plays in Christianity.
Unlike Christianity or Islam, Judaism is not assimalitve in nature and does not try to actively convert members of the non Jewish population to Judaism. As such with a few exceptions, Jews have lived as a minority religion among other populations for the last 2000 years.
Over the last 2,000 years the Jews as a people have have been targets of negative mythology and prejudices, especially in the Christian world, although recently this has shifted more to the Islamic world. These stem from religious reasons, cultural bigotry, class conflicts, legal discrimination, scapegoating, stereotype and -- after the 19th century -- pseudoscientific racial theories and conspiracy theories (many of which originated with fabrications created by the Tsarist secret police to further the reactionary agenda of Tsar Alexander III).
This bigotry is collectively known as antisemitism and is for the most part completely unfounded, with what little that does have some foundation in reality being the result of imposed conditions. For example, Jews had a reputation as moneylenders and bankers, which in medieval Europe was often one of the few economic activities in which Jews were allowed to engage and one which Christians were barred from doing because of scripture against usary (which are also present in the Torah, with jews being under more of an obligation to follow them).
These beliefs were historically mainly established in the Christian World, although after the second world war due to factors involving the state of Israel and the Grand Mufti Haj Amin al-Husseini (who collaborated with the Third Reich) they have shifted to the Islamic world. Antisemtism has been on the decline in the west ever since World War II, but is still present.