Anything you plug into a computer

A) attachment
B) back up
C) boot
D) CPU
E) domain
F) file
G) hardware
H) input
I) interface
J) memory
K) modem
L) output
M) peripheral
N) prompt
O) server
P) software

Peripheral

Relating to or situated on the edge or periphery of something; in computer terms, it refers to devices connected to a computer system externally.

Plug Into

To connect or become involved with something or someone in a direct or significant way.

Computer

An electronic device capable of processing information according to a set of instructions, used for a wide range of tasks.