Firmware is data that is stored on a computer or other hardware device's read-only memory (ROM) that provides instruction on how that device should operate. Unlike normal software, firmware cannot be changed or deleted by an end-user without the aid of special programs and remains on that device whether or not it's on or off.
A firmware update is a software program that can be used to update the firmware in these devices. For example, a user could download a firmware update for a network router that enhances its capabilities or fixes an issue. Firmware updates are available from hardware manufacturers. In some cases, computer enthusiast websites create their own firmware updates to give a device even more capabilities than the manufacturer intended.
Note: These updates are usually not supported by the manufacturer.