Universal joints, also known as U-joints, are mechanical couplings used to transfer power between two shafts, even when their axes are at an angle. They allow for the transmission of rotary motion and are used to connect shafts that may not be perfectly aligned. Universal joints can handle slight misalignments in shafts and can be combined to correct for larger misalignments. They enable rotation in any plane, making them suitable for applications where shaft orientation changes. Common uses include drive shafts in vehicles, industrial machinery, and other situations requiring flexible and versatile couplings.