Firmware is software that is embedded in a piece of hardware. You can simply think of it as "software for hardware." However, software is different from firmware, so the two are not interchangeable terms.

Devices that you might think of as purely hardware, such as an optical drive, network card, TV remote control, router, media player, camera, or scanner, all contain software programmed into a special memory within the hardware itself.

CD, DVD, and BD drive manufacturers regularly release firmware updates to keep their hardware compatible with new media.

For example, imagine you buy a 20-pack of blank BD discs and try to burn a video onto a couple of them, but it doesn't work. One of the first things the Blu-ray drive manufacturer would probably suggest is to update/flash the firmware on the drive.