voluntary

This term carries a strong sense of agency and choice. It suggests an action taken without coercion, pressure, or external mandate, often evoking a spirit of generosity or civic duty when used in social contexts. It implies a conscious decision to opt-in to a task or a commitment. In a medical or biological sense, the word shifts from a moral or social choice to a physiological one. Here, it describes the difference between movements you control, like walking, and those that happen automatically, like a heartbeat, removing the element of "will" in the psychological sense and replacing it with neural control.