Not To Be Confused With
Efficacious (or 'effectual') grace certainly achieves conversion; 'sufficient' grace (in some Catholic debates) is enough to enable but does not by itself ensure the response. The distinction is central to grace-and-freedom debates.
The term features in both Reformed theology and the Catholic Thomist-Molinist debates over how grace moves the will without destroying its freedom. All sides affirm grace's necessity; they differ on how grace and the free response relate so that the act is both God's gift and truly the person's own.