What is the choice of Numeraire?

What is the choice behind Numeraire? Is it a specific cryptocurrency or a framework that allows for the selection of different digital assets? If it's a specific coin, what makes it unique and why has it been chosen as the foundation for the platform? Alternatively, if it's a framework, how does it work and what factors influence the choice of the underlying asset? Understanding the choice behind Numeraire is crucial to evaluating its potential impact and usefulness in the world of cryptocurrency and finance.