Ge 6:4 There were giants (Nephilim in Hebrew) on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore children to them. Those were the mighty men who were of old, men of renown.
The word "giants" here in Hebrew is Nephilim. There are some who say that Nephilim here does not really refer to men of gigantic physical statures but giant in terms of ferocity and wickedness. I believe that this refers to giants in a physical sense. Elsewhere Moses used the word Nephilim and you can read it for yourself. I am quoting from the ESV:
Gen 6:4 The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of man and they bore children to them. These were the mighty men who were of old, the men of renown.
Num 13:32 So they brought to the people of Israel a bad report of the land that they had spied out, saying, "The land, through which we have gone to spy it out, is a land that devours its inhabitants, and all the people that we saw in it are of great height.
Num 13:33 And there we saw the Nephilim (the sons of Anak, who come from the Nephilim), and we seemed to ourselves like grasshoppers, and so we seemed to them."
