Freedom is the absence of physical coercion.
In a political context, freedom means to live in a social system based on the protection of individual rights, or negatively: freedom from the initiation of physical force. Initiation means those who start the use of force to achieve their ends, i.e., a bank robber.
To live (act) rationally (by reason) in society in order to survive and prosper, the individual needs one thing from his fellow citizens: freedom. The freedom to use one mind to select those actions necessary to sustain one’s life by acquiring, possessing and using property (the physical means of sustaining one’s existence), neither sacrificing oneself to others nor sacrificing others to oneself. According to Ayn Rand:
“Since knowledge, thinking, and rational action are properties of the individual, since the choice to exercise his rational faculty or not depends on the individual, man’s survival requires that those who think be free of the interference of those who don’t. Since men are neither omniscient nor infallible, they must be free to agree or disagree, to cooperate or to pursue their own independent course, each according to his own rational judgment. Freedom is the fundamental requirement of man’s mind.” 
It is this freedom that unleashes the creative potential of the individual, resulting in a society of universal peace, continuous progress and boundless prosperity.
 Ayn Rand, “What is Capitalism?” Capitalism: The Unknown Ideal