Hardware refers to the physical components of a computer — the ones you can touch. Examples include the keyboard, the monitor, and the printer.
A header file is a file that contains class interface definitions and/or global function declarations. By convention, header files have the extension .h.
Hex is a shortened form of hexadecimal.
A hexadecimal number system has sixteen digits, '0' through '9' and 'a' through 'f'.