The phrase "quiver full" comes from Psalms 127: 3-5:
Lo, children are an heritage of the LORD: and the fruit of the womb is his reward.
As arrows are in the hand of a mighty man; so are children of the youth.
Happy is the man that hath his quiver full of them: they shall not be ashamed but they shall speak with the enemies in the gate.
Being 'quiver full' is just a way of saying that we trust the Lord to bless us with children as He wills. That's the short and simple answer to the "What is quiverfull?" question.
