It means “judgment” “he judged” in Hebrew. In the Old Testament Dan is one of Jacob’s (Israel’s) twelve sons by Rachel’s handmaiden, Bilhah, and the founder of one of the twelve tribes of Israel. His name is explained in Genesis 30, 6.

Dan was called by Rachel who exclaimed, “GOD has judged me, has indeed heard my voice, and has given me a son” (Genesis 30, 6). Later, Jacob, his father gathered his people around his deathbed, saying, “Dan will judge his people, as one of the tribes of Israel” (Genesis 49, 16).

Because of the Book of Judges, in Micah’s account of the Idol, which describes the tribe of Dan as having used the ephod and teraphim in worship, and Samson (a member of the tribe of Dan) being described as a Nazirite, the classical rabbinic writers concluded that Dan was considered a black sheep.
In the apocryphal Testaments of the Patriarchs, Dan is depicted as the one who hated Joseph, and he was the one who invented the idea of deceiving Jacob by smearing Joseph’s cloak with the blood of a kid (Testament of Dan 1,
Testament of Zebulun 4 and Testament of Gad 1). In the apocryphal Prayer of Asenath, Dan is portrayed as plotting with the Egyptian crown prince, against Joseph and Asenath. In Jacob’s Blessing, Dan is described as a serpent, which seems to have been interpreted as a connection between Dan and the tempter, a connection made in the apocryphal Testament of Dan.

Early Christian writers, such as Irenaeus and Hippolytus, even believed that the Antichrist would come from the tribe of Dan, drawing the belief from a verse in the Book of Jeremiah that states “the snorting of the horses was heard by Dan.” (Jeremiah 8, 16)

The apostle John omits the tribe of Dan when he mentions the twelve tribes of the children of Israel, regarding the 144,000 Israelites, reporting the tribe of Joseph twice (being represented by Manasseh as well).