Things – every’thing’, actually – are/is relative.
Relative to the agent evaluating each of those things.
Accordin’ to Einstein, that is.
He was the one who taught us to use whatever reference frame suits our needs.

Do you reckon anybody wasted any time or energy thinking about freedom before the advent of slavery?
Me neither.
Forget about the fact that, in those times, people didn’t have much time left for abstract thinking. Finding food and enjoying it with friends kind of drains your energy when you have to do it yourself… The point being that, in those times, everybody was free. Hence ‘had’ nothing to compare freedom with… No lack of freedom, no reason to speak/think about it.
No reason to notice the thing and no reason to coin the concept…

Hunter-gatherers have no use for ‘property’. Personal objects are just that and everything else either belongs to Mother Nature or to the entire group. And this goes without saying. Or thinking about it. People share everything as a matter of fact and common sense discourages the others to use anybody’s personal objects unless in an emergency.
Agriculture – either herding animals or growing crops – changed everything. Property, both as a concept and as an everyday manner of dealing with ‘things’, was invented and introduced in daily use. Productivity increased dramatically. Which made it possible for people to have ‘spare time’. For thinking.
And for planning…

‘The neighbors have better crops. Let’s go take some for us. And while we’re at it, let’s take some of their women too’.
The first slave was probably the first person to long for freedom…

‘Cheap’ slave work coupled with the increased social productivity induced by a markedly improved technology for obtaining food meant that some individuals could afford the luxury of thinking.
The Ancient Athenians had both slaves and philosophers. The slaves did whatever was needed to be done while some of the ‘beneficiaries’ had enough time, and energy, to let their minds ‘free’. To roam free in search for meaning.
To coin the concept and to explore freedom…

Relative “To whom”? To us!
We’re responsible for freedom and freedom is relative to us.
We have invented it. We’re the ones using it. In the sense that we’re the ones who need to notice that freer communities fare a lot better than the less free.

So freedom is relative both to those thinking about it and to each particular community.
To each particular community which puts freedom into practice!