(Hebrew גברים) Literally, "heroes, mighty ones, valiant ones" but this must be understood in context, since the word can refer to actual heroes (related to the sephirah Geburah), or to those who have fallen from that state.
"There were נפלים Nephilim ["giants," another type of fallen angel] in the earth in those days; and also after that, when the sons of God [angels, bodhisattvas] came in unto the daughters of men, and they bare [children] to them, the same [became] גברים [Giborim, "mighty men"] which [were] of old, men of renown. And GOD saw that the wickedness of man [was] great in the earth, and [that] every imagination of the thoughts of his heart [was] only evil continually." - Genesis 6
The Zohar describes five types of fallen angels; one of them are called Giborim who "built organizations, colleges, and founded oracles and temples, not for the worship and glory of the Holy One, but for their own self-exaltation, and then tyrannized over [the archetypes of] Israel as though they were dust of the earth, by plundering and robbing them of every thing they possessed."
Learn more about the Zohar: Fallen Angels.