The identity of the נְּפִלִים (něpîlîm) is a matter of considerable speculation. It has often been suggested that their name might have been derived from the fact that they were the sons of the semi-divine beings referred earlier as the בְנֵי־הָאֱלֹהִים (běnê hā’ělōhîm). Another conjecture suggests the Nephilim were the children of “the fallen ones” who “fell” נָפַל (näpäl = “fall”) from heaven, hence they were “fallen angels.”
With respect to the first two theories, if this forbidden co-mingling between the human and the heavenly realm is at the heart of the narrative, then once again the Torah is stressing how human beings seem to continue violating the moral boundaries governing its existence (cf. Gen. 3ff and 4ff).
A third theory argues that the Nephilim and the בְנֵי־הָאֱלֹהִים were one and the same. Their huge, powerful presence instilled fear into the hearts of the enemy soldiers, causing them to fall at the battlefield or in their presence. They utilized intimidation and fear to obtain whatever they wanted. The verb נָפַל (näpäl = “fall”) is often used in association with a military assault. Regardless of whether one wishes to believe that they were “fallen angels” or just “fierce warriors,” these people made the earth autocratic, where only the aggressive and the strong ruled. The Nephilim imposed a gangster-like rule over the masses wherever they went. Rashi’s pithy Midrashic statement probably sums it up best: “They were men who brought destruction and desolation into the world.”
Biblical scholarship since the time of Ibn Ezra has raised an intriguing question: Did these people survive the Flood? It would seem based on the verse in Numbers 13:33 that they did. Did they later become the aboriginal inhabitants of Canaan, living at the time of Moses? Ibn Ezra and Rashi suggest that they might have survived. It is much more likely, though, that the words of the spies were deliberately exaggerated so as to induce fear in their listening audience. This use of hyperbole is consistent with their concluding remarks about the Land of Canaan “and to ourselves we seemed like grasshoppers, and so we seemed to them” (Num. 13:33).That is to say, the spies evoked the memory of the Nephilim even though they had long perished centuries before.
Alternatively, the term “Nephilim” may be a generic term referring to anyone who is of a tall and mighty stature. Personally, I am partial to this particular interpretation. The 20th century Israeli biblical scholar U. Cassuto further argues that these warriors may have been called “Nephilim” because of the common fate these warrior peoples shared, for ultimately they both “fell” to their own destruction, either during the Flood or during the Israelite conquest and violence. Cassuto draws a direct allusion to Ezekiel 32:12, which also speaks of theגִּבּוֹרִים (gîbôrîm = “the mighty warriors”) who had descended to Sheol.
 Ibn Ezra, Keter Torah. Interestingly enough, Symmachus renders Nephillim as bivaioi, “violent ones.” For other examples of this nuance in the Tanakh, see Jer. 48:32; Isa. 16:9; Josh.1:15; Judg. 15:18.