The word “giant” in Eng. may have two meanings. It may refer to a race of beings of superhuman size and strength who appear in the mythology and folklore of most ancient peoples, often at war with the gods; or it may be used to refer to human beings of abnormal and unusual size, usually due to a disease of the pituitary gland, properly referred to as “gigantism.” In modern times medical accounts record a woman 8 ft. 4 1/2 in. tall, while claims have been made in modern times of giants as tall as 9 ft. 3 in. That “giants” occur in the OT in the latter sense admits of no doubt. Goliath of Gath, whom David slew, was “six cubits and a span” in height (1 Sam 17:4). If the ordinary cubit (q.v.) is meant, this represents a height of c. 9 1/2 ft. Compare also Og, king of Bashan, whose “bed of iron” was 13 cubits long and 4 cubits wide (13 ft. x 5 ft.) (Deut 3:11), and the Egyp. whom Benaiah slew, who was 5 cubits tall (c. 7 ft. if the ordinary cubit is meant, 1 Chron 11:23). 2 Samuel 21:15-22 records the exploits of David and several of his men against Philistine giants (although only one is said to be “a man of huge stature,” 2 Sam 21:20; 1 Chron 20:6).

The only passage that may refer to giants in the first sense is Genesis 6:1-4, where the Nephilim (q.v.) are mentioned. Many hold that this passage refers to the stories of giants on earth who are descended from union between gods and humans and that it is used by the author (chs. 1-11) as a measure of the effects of human sin (see, e.g., Von Rad, Genesis, Philadelphia: Westminster [1961], pp. 109-112).

International Standard Bible Encyclopedia (1915)

In the first two cases the Revised Version (British and American) changes "giants" into the Hebrew words "Nephilim," nephilim, and "Rephaim," repha’im, respectively (see these words). The "Nephilim of Ge 6:4 are not to be confounded with the "mighty men" subsequently described as the offspring of the unlawful marriages, of "the sons of God" and "the daughters of men." It is told that they overspread the earth prior to these unhallowed unions. That the word, whatever its etymology, bears the sense of men of immense stature is evident from the later passages; Nu 13:33. The same is true of the "Rephaim," as shown by the instance of Og (De 3:11; Jos 12:4). There is no doubt about the meaning of the word in the ease of the giants mentioned in 2Sa 21 and 1Ch 20.