CIA (Complex Interface Adapter) refers to the MOS Technology 8520 chips used in Amiga computers to handle input/output operations, timers, and peripheral interfacing. Two CIAs were typically present in Amiga systems: one managing the keyboard, floppy disk signals, and serial port, while the other handled parallel port, mouse/joystick ports, and additional timers. These chips were successors to the 6526 CIA used in Commodore 64 computers and provided essential system timing and interrupt handling capabilities.