The phrase "elbow grease" refers to hard work or effort put into a task. It is often used figuratively, suggesting that one must exert physical force or energy in order to achieve something. The term comes from the idea that when you use elbow grease (i.e., rubbing your elbows together) to lubricate an object, it becomes easier to move and manipulate. In a broader sense, "elbow grease" can refer to any type of effort or hard work put into achieving something, whether physical or mental.