Initially, I wrote that I would spend the rest of my life trying to answer the question of what freedom is. However, now, I think there are a few approaches to answering this question.
I would consider freedom to ultimately be a situation wherein everyone is capable of living without domination. At some point in human history, humans were free. Now, we are not.
However, most would consider freedom and liberty mutually interchangeable. As a communist, I am uninterested in liberty, as liberty is the right to do things within the context of a liberal state. Liberty might therefore be considered a subset of freedom.
Freedom, if defined as freedom from domination, then, is something broader.