Who were the Nephilim?
"Nephilim" is translated "giants" in the King James Version, but retained in the Revised Version (British and American), is found in two passages of the Old Testament--one in Genesis 6:4, relating to the antediluvians; the other in Nu 13:33, relating to the sons of Anak in Canaan.
In the former place the Nephilim are not necessarily to be identified with the children said to be borne "the daughters of men" to "the sons of God" (Gen 6:2,4); indeed, they seem to be distinguished from the latter as upon the earth before this unholy commingling took place.
But it is not easy to be certain as to the interpretation of this strange passage. In the second case they clearly represent men of gigantic stature, in comparison with whom the Israelites felt as if they were "grasshopers."
This agrees with Gen 6:4, "the mighty men that were of old, the men of renow." Septuagint, therefore, was warranted in translating by Grk: gigantes.
IBSE, "Nephilim" (in the public domain) with minor edits.