Judaism is a monotheistic religion and its followers are normally called Jews. It is commonly viewed as an ethno religion and there are even Jews who claim to be atheists but still identify as Jews. But Judaism is the religion of the Jews and they follow the Old Testament and the Talmud as their religious sources. Its followers are considered followers of the Prophet Moses(as) and they believe that the first five books of the Old Testament is the Torah. They have similarities with Islam and they are the closest to us in faith. They share the same concept of God and orthodox Jews consider God as the law giver and they must obey him.
Jews believe that they must live, rule and judge according to the laws of God which they believe is the Old testament. Their believes make them very similar to Muslims in many ways but we do not believe that the modern Bible is the actual Torah that was given to the Prophet Moses(as). Jews further believe in the prophets mentioned in the Old Testament and they reject Jesus(as) and Muhammad (saaws). The name "judaism" derivbes from Judah who was one of the sons of the prophet Jacob(as). So it is like a nick name for the tribe of Judah but today it is used for Jews in general.
The term is used in different ways so it is a little complicated because they have used different names in different times. For example, Moses(as) was not of the tribe of Judah but he was a Levite and in his time the name Judah or Judaism wasn't used yet or adopted. It is similar to christianity and how the name didn't exist in the time of Jesus(as) but was given by outsiders and later adopted by the followers of Paul who became known as "Christians". In the ancient world they were known as Hebrews, Israelites and later Jews. It kind of depends on which time period one speaks of but in general today Judaism is the name of the religion of the Jewish people and they are considered followers of Moses. I hope this kind of helped you out a little and let me know if you need more info but I am sure other brothers/sisters can help further inshaAllah.
Waleykom salaam
