voluntariness; voluntary nature; optionality
Abstract noun referring to the quality of being voluntary, optional, or at one's discretion. Often used in legal, philosophical, or technical contexts.
Participation in this system is highly voluntary.
We discuss the voluntary nature of the contract.
Compound of 任意 (にんい, 'voluntary, optional') + 性 (せい, '-ness, -ity'), forming an abstract noun meaning 'voluntariness' or 'optionality'.