“Ne-fi-lim” is the plural form of the word “Na-fil.” Since Nefilim appears only twice in the Bible, all scientific, linguistic, philological and theological assertions concerning who they were are limited to what we can learn from these two verses.
It is almost certain that this word is related to the root verb “na-fal,” which means “to fall.” When you listen to the sound of the narration, you’ll surely notice that the English “to fall” is related to the same Hebrew origin.
The first reference, found in Genesis 6:4, gives us a clue which further substantiates the idea that the Nefilim fell to earth (the English earth also comes from the Hebrew “e-retz”) from heaven: “There were Nefilim in the earth in those days; and also after that, when the sons of God came in to the daughters of men, and they bore children to them, the same became mighty men of old, men of renown.” The verse mentions that the Nefilim were on earth.
Were they from elsewhere then?
The mentioning of “the sons of God” in the same verse and in verse 2 as well gives an extra clue to the place from which they came (fell) to earth.
The second place where the Nefilim are mentioned is in Numbers 13:33. “And there we saw the Nefilim, the sons of Anak, who come from the Nefilim; and we were in our own sight as grasshoppers, and so were we in their sight.” We learn from here that the Nefilim were giants.
There are several theological explanations to the presence of the Nefilim. Some claim that they were angelical entities. Others contend that they were demonic creatures. Either way, “the sons of God” is a problematic term for the Judeo-Christian principles of faith. It seems that at least for the near future we’ll continue to rely on speculations rather than on solid facts regarding these mysterious entities.