The term 'PART OF IOS' can be solved by two crossword solutions: SYST (4 letters) and SYS (3 letters). SYST stands for System Software, which is the core software of Apple's iOS operating system. It is responsible for managing the device's hardware and providing basic services for other applications. SYS stands for System, which is the main component of the iOS operating system. It provides the user interface, manages memory, and handles input/output operations.