Fuse Bits?

I've been looking around trying to find out what fuse bits are and haven't come up with a concise answer. In the ATMega Datasheet, it only showed that they were used to set the clock source (and maybe a few other things) but what ARE fuse bits? Like why are they called that, where are they stored, and what do they do? Also, is fuse bits a universal term for configuration bits at a specific address or is it just for ATMegas or AVRs?

Do like everyone less does use google !!!

“Avr + fuse bits”

but what ARE fuse bits

Bits in an internal register of the processor, not accessible to a program running on that processor.

Like why are they called that,

In early processors they were actually miniature fuses that you could open by passing a large current through it. That's why we talk of blowing a program. Early PROM was full of fuse links you literally blew open to get your bit pattern. Of course nowadays they are not like that but made from flash memory that can be reset.

what do they do

Set any over arching probity of the processor, as defined by the manufacturer. Like code protection to stop someone reading the code out of an embedded system.

is fuse bits a universal term for configuration bits

Many processors use this term and virtually all use the concept.