I'm being confused by the use of firmware in the context of Linux.
My understanding of firmware & driver is that firmware is the code that runs on the bare metal of a device such as a Bluetooth IC, or keyboard controller, or video card, or a single-purpose micro-controller. The firmware exposes an interface for the OS to use its services.
The driver, in comparison, is the software that the kernel uses to communicate with previously mentioned interfaces provided by the firmware. Thus, a video driver, a keyboard driver, a bluetooth radio driver.
So why is it that I keep reading about Linux firmware files having to be installed (e.g. here). Do these get uploaded into the hardware? Are these files used by the kernel? What is the meaning of firmware in this context?