Concise Bible Dictionary:

Besides the common use of this as “chief,” referring to the heads of families and heads of tribes, the word was used symbolically of government and power, as when God declared that the Seed of the woman should bruise the serpent’s “head” (Gen. 3:15). In the New Testament the term κεφαλή is employed for the relative position of man in nature, and of Christ and of God: the head of the woman is the man; the head of every man is Christ; and the head of Christ is God (1 Cor. 11:3). In another connection Christ is the head of the church (Eph. 5:23; Col. 1:18); and He is head over all things to the church (Eph. 1:22; Col. 2:10). As head of the church Christ removes entirely every other controlling or guiding authority. As the head of a man guides and controls his body, so Christ has the complete control over His church.
In Revelation 12:3 the “head” symbolizes a form of power or kingdom; and in Revelation 17:3,9, the seven heads are seven mountains on which the woman sitteth, representing Rome, which was commonly described as built upon seven hills, and the woman signifies Papal Rome.