The term 'PART OF A ROTATING SHAFT' can be summarized as a CAM, which is a three-letter word. A CAM is a rotating or sliding piece in a mechanical linkage used to transform rotary motion into linear motion or vice versa. It is often used in engines and machines to convert rotational motion into linear motion. Cams are typically used to open and close valves in internal combustion engines, and they are also used in other mechanisms such as pumps and compressors.