How do you define "free will" and where is that concept as you define it taught in the Bible?
I define it as you might expect, and quite broadly: that humans have the capability to choose their own actions, and that includes the ability to choose to do things either according to God's will, or against it.
Within the context of TULIP theology (or at least FR discussions about it), "free will" has been said to apply to the ability to choose for or against belief in God, because a free-will choice to "repent and believe" would supposedly make man an agent of his own salvation.
Logically, however, that superficially limited constraint quickly leads to what one might call the "strict pre-destination" position: humans can have no free will about anything, as to allow it would mean that God is "not in control".
and where is that concept as you define it taught in the Bible?
Being made in God's image and likeness (Genesis 1:26) is a pretty good place to start (unless you want to deny that God has free will...). The Fall would show human free will in action. And the very fact of sin requires that humans have the ability to choose against God's will; to hold otherwise makes the concept of "sin" completely meaningless -- not to mention that it essentially makes "sin" an expression of God's will.