WordNet (r) 3.0 (2006):

firmware
    n 1: (computer science) coded instructions that are stored
         permanently in read-only memory [syn: firmware,
         microcode]

The Jargon File (version 4.4.7, 29 Dec 2003):

firmware
 /ferm'weir/, n.

    Embedded software contained in EPROM or flash memory. It isn't quite
    hardware, but at least doesn't have to be loaded from a disk like regular
    software. Hacker usage differs from straight techspeak in that hackers
    don't normally apply it to stuff that you can't possibly get at, such as
    the program that runs a pocket calculator. Instead, it implies that the
    firmware could be changed, even if doing so would mean opening a box and
    plugging in a new chip. A computer's BIOS is the classic example, although
    nowadays there is firmware in disk controllers, modems, video cards and
    even CD-ROM drives.


The Free On-line Dictionary of Computing (30 December 2018):

Firmware

   Software stored in read-only memory (ROM) or programmable ROM
   (PROM).  Easier to change than hardware but harder than
   software stored on disk.  Firmware is often responsible for
   the behaviour of a system when it is first switched on.  A
   typical example would be a "monitor" program in a
   microcomputer which loads the full operating system from disk
   or from a network and then passes control to it.