Plain-English definition
Basic Input/Output System. The fundamental firmware that initializes hardware when a computer boots up before loading the operating system.
Example in context
“Updating the Bios is generally only recommended when specifically directed by the manufacturer to solve a known issue or support a new CPU.”
Where you may see this term
You may see the firmware name on the first startup screen, in the System Information utility, or on a computer maker’s download page. Newer computers often use a Uefi interface while still using the familiar Bios label in menus and documentation.
Practical guidance
Record the computer or motherboard model and current firmware version before considering an update. Use only the package and instructions published for that exact model. Keep the computer connected to reliable power and do not interrupt the update, because incomplete firmware can prevent startup.