If you are referring to the nickname of an ancient rabbi, Elisha ben Avuyah (×לישע בן ×בויה‎), also known as "Acher", "The Other", he was a religious authority born in Jerusalem sometime prior to the year 70 CE.
Otherwise, There is no such concept in Judaism.
In Judaism, "the other" refers to someone who is different or outside of the Jewish community. It can refer to individuals of different religious or ethnic backgrounds. Judaism teaches the importance of treating the other with kindness, respect, and inclusivity, as exemplified by the commandment to "love your neighbor as yourself."
Back when Judaism was first Founded, all other religions were polytheistic. Judaism was monotheistic.
Among other differences, Judaism is monotheistic.
No, one is an Abrahamic religion (Judaism) and the other is an Indian faith.
Unlike other religions, Judaism is not centralised and there is no one leader.
Judaism was the only belief that abhorred idolatry.
Judaism doesn't have 2 sides. It has many many aspects.
Among other differences, Judaism is monotheistic.
Christianity and Islam are the two major ones, but there have been several other offshoots of Judaism.
Jewish Faith
Christianity.
The teachings of Judaism can be found in the The Hebrew Bible, the Mishna, The Talmud, and many other texts.
Usually if you are of Hebrew descent, your religion is Judaism, but not always. There are approximately 500,000 Jews in the world who practice religions other than Judaism.