from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The set of routines stored in read-only memory that enable a computer to start the operating system and to communicate with the various devices in the system, such as disk drives, keyboard, monitor, printer, and communications ports.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- Built-in operating system.
- Basic input/output system.
from The Century Dictionary and Cyclopedia
- n. Living things considered collectively and in contrast with things that are not alive.
b(asic) i(nput/)o(utput) s(ystem).(American Heritage® Dictionary of the English Language, Fourth Edition)