My personal definition of free will is my ability to be the prime mover of all my practical actions.
I am a physical being bounded by my physical and psychological needs, but I can choose and apply as I deem required by my free will.
Now to some it appears these limitations mean we loose our free will, but if I can choose to take my life or to protect it, that is my choice. If another motivation or experience comes along that changes my direction or feelings or viewpoint, I can choose to follow this. If these experiences like taking LSD change my life, over which I have no choice, I did have choice to start the cascade.
It strikes me people want total control on the effects of influences, and this lack of control then means they are determined by things that take their life and direction away from them. This is just the boundary of you reap what you sow, action and reaction, consequences of what you do change everything.
Daily optimism keeps us working forward to meet certain goals, but because we choose to walk this path, it is our free will trade off to achieve this goal. But is a real sense we are slaves to our own biology and requirements, so the impression we can choose is very real, but it is not as open as we would like, though this does not deny it actually exists.
Deteminists say they have no free will, like Sam Harris, yet it appears their lack of free will appears to be different from the free will I am talking about. So do people hold the view of free will, or its apparent action, yet believe it is just an illusion?
It appears that what we are talking about is moral agency, guilt and responsibility for evil actions on the individual and social circumstance. Are we guilty of sin, or just it is inevitable because of who we are?
Sam Harris summary views Free will introduction