Devices in AmigaOS are software modules that provide standardized interfaces for hardware access and abstract specific hardware details from applications. They communicate through the Exec messaging system, allowing programs to send commands and data via standard I/O requests without needing to know low-level hardware specifics. Key examples include serial.device for serial ports, trackdisk.device for floppy drives, and printer.device for printer output, forming a crucial layer of AmigaOS's hardware abstraction architecture.