Opportunity could be defined in so many ways. There's one way of defining it, equality of opportunity, which is in fact the equality of capability, but the libertarians got there first and they have - like the Americans getting onto the moon, naming every crater after something like an astronaut - they have got there and named "opportunity" in a way that we cannot get ownership of now.
Amartya SenThe notion of human right builds on our shared humanity. These rights are not derived from the citizenship of any country, or the membership of any nation, but are presumed to be claims or entitlements of every human being. They differ, therefore, from constitutionally created rights guaranteed for specific people.
Amartya Sen