Act for Definition 1 of 3Pro Tip 1/3Temporary Replacement Used when someone temporarily takes over another person's responsibilities. Sara will act for me while I recover from surgery. Pro Tip 2/3Not a Promotion Does not mean the person has been promoted, only covering duties temporarily. He's only acting for the supervisor this week. Pro Tip 3/3Expectations Clarity Clear communication of the acting role's expectations prevents misunderstandings. Before acting for her, clarify what tasks you're responsible for.