It is one of the characteristics of man created in the image of God that distinguishes him from all the rest of creation. Without freedom, man would not be truly human. But at the same time it is an exceedingly perilous gift because he can use that freedom to disobey God and so fall into sin. No animal, below man, is able to sin, because no subhuman creature is truly free. It acts in terms of stimuli and responses, heredity and environment.
Man however is created to act freely.
Much of his action is determined as is the animal s, but essentially man, like God, is free to make decisions, free to act. If he uses that freedom at any point to disobey his Creator, he thereby sins. A good definition. So it is throughout the Bible. For example, the Ten Commandments are given by God.