voluntary

To emphasize that there is absolutely no obligation or compulsion.

To emphasize that something is wholly based on free will.

To highlight that the action is motivated only by choice, with no other factors.

To assert firmly that participation is not required and is based on choice alone.

To indicate that something is mostly, but not entirely, based on choice.

Used to describe the state of something being optional or done by choice.

Used to describe something continuing to be optional or based on choice.