Active Coils in a spring
The active coils are what make a spring a spring. We normally refer to the coils that open in an extension spring, the coils that deflect or close in a compression spring and the coils that twist or wind up/down in a torsion spring as "active". The active term should really be applied to any portion of a spring that stores and releases energy. In a straight lever, the portion that flexes would be considered active.